Back in July, I wrote about the types of digital music services that are available to consumers and the emergence of two cloud-based services, Amazon Cloud Player and Google Music, which threatened to change everything. (See Thinking About Digital Music Services for more information.) Since then, I've used both of those cloud services quite a bit, and have come to understand their basic strengths and weaknesses. As important, Apple's stellar iTunes Match has just recently shipped as well. And what I've discovered is that it doesn't make sense to limit yourself to just one service. Indeed, the best strategy might in fact be to use all three, or perhaps two of the three, in tandem.

This assumes, of course, that you maintain your own local collection of music, which you sync to devices and, perhaps, stream throughout your home.

As a refresher, there are basically three types of digital music services available today. These include a la carte music services like iTunes and Amazon MP3, digital radio services such as Pandora, and digital music subscription services like Rhapsody, Zune Pass, and Spotify.

You can of course, use any combination of these services, though they don't really integrate with each other in any meaningful way. I purchase songs at both iTunes and Amazon MP3 fairly regularly, for example, and also subscribe to the paid version of Pandora. Each serves its own purpose and each is used separately from the other.

If you do maintain a collection of your own music--that is, music you've ripped from CDs, purchased from a la cart services, or obtained in other ways (file sharing services, etc.) and store on a PC's hard drive, then there's a new set of useful cloud computing services that makes this collection far more portable and useful. The first two, Amazon Cloud Player and Google Music, are what's called digital lockers because they're both essentially just cloud-based storage with music player front-ends. They're comparable, though each has a few features the other lacks, which makes picking a winner difficult. (I happen to prefer Amazon Cloud Player, which is a lot nicer looking. But Google's offering lets you edit song meta data, something that's not possible on Amazon's service.)

(Read my preview of Google Music and my review of Amazon Cloud Drive and Cloud Player for more information about those services.)

The most recent new cloud computing service, iTunes Match, turns things around a bit. It, too, is essentially a digital locker, but unlike the other services, it doesn't require you to upload your own collection. Instead, iTunes Match scans your iTunes-based music collection, compares the songs it contains against the iTunes Store's voluminous collection, and then provides you with cloud-based access to those songs instead. Apple will upload the few songs iTunes doesn't contain as part of the process, giving you access to your entire collection in the cloud.

(Read my review of iCloud for more information about iTunes Match.)

Apple's approach has two advantages over traditional digital lockers. First, you don't need to upload your entire music collection. In my case, that represents a 37 GB collection of about 4800 songs (including some little-used music like my Christmas songs).  Second, because Apple is providing you with its own versions of your songs, the cloud-based iTunes Match version of your library isn't a mishmash of different file types and songs with varying quality; instead, everything is in pristine, high-quality, 256 Kbps AAC format. This is a chance to not just go legit--if you used file sharing services--but to really clean up your collection. I was happy to do it.

Apple's service has a few other advantages, too. If you use any Apple mobile devices, or iTunes on a PC or Mac, or an Apple TV, your entire music collection is now instantly available from anywhere. Apple doesn't really provide song streaming functionality, however, like Amazon or Google. Instead, you need to download them to your device. But they can play semi-instantly as they download. Since so many people use iPods, iPhones, and iPads, this alone makes iTunes Match very desirable.

But iTunes Match comes with a hidden benefit, and this is where using this service in tandem with Amazon Cloud Drive or Google Music starts to make a lot of sense. And that is that you can actually download your entire music collection from iTunes Match to a different PC. And the copy of your collection that you get on that other PC is nicely organized and consists of high-quality, 256 Kbps AAC files. And once you've downloaded the entire collection, you can turn around and do something very interesting. You can then upload it to either Amazon Cloud Drive or Google Music. Or both.

Which is exactly what I've done.

The first step, of course, was to remove all of the content I had already uploaded to Cloud Drive and Google Music. You may recall from my earlier write-ups of these services that I had uploaded my main music collection, about 24 GB worth, to both. But since doing so, I hadn't really kept them in sync with my PC-based collection, though I did use the web and Android clients to access them online from time to time. Part of the problem was that some of the music wasn't properly tagged, so instead of seeing proper song names and other information for these songs, I saw the file name in the song field, like 01 Song name. So I was happy to blow away these cloud collections and start over.

Doing so is a bit ponderous. Amazon Cloud Drive lets you multi-select songs much as you do with files in Windows Explorer. But if you select and then try to delete more than 500 songs at a time, it will warn you that 500 is the limit and offer to just delete the first 500 of your selection. Once this was figured out, moving through the collection and deleting the whole thing took a few minutes. In Google Music, there is actually a handy Delete My Library button in Settings, Music Settings. But it's not immediate, and the warning dialog says it could take a few hours. So I clicked the button and let it sit before proceeding.

Once I cleared out the old collections, I could proceed as if I had never used either service. So if that's the case for you, this is where things pick up again. I then uploaded this new, near-pristine copy of my music collection to first Amazon Cloud Drive and then, a day later, to Google Music. The upload process was slow, taking about 12 hours for Amazon and almost 24 for Google. But once it was done, I had a near-perfect version of the collection in both cloud libraries.

I say "near perfect" because neither version is the full collection. On the PC, iTunes reports 4804 songs, but Amazon says there are 4800 songs in its version of the collection, and Google Music says 4708. The Amazon one I can live with. But why did almost 100 songs not get uploaded to Google?

Interestingly, Google's music uploader reported that some songs weren't uploaded. But it said only 9 couldn't be uploaded, not about 100. And according to the failure list, in each case it was because the files contained "no music." Intriguingly, some of these songs weren't uploaded to Amazon either. And these songs won't play in iTunes, so there is indeed something wrong.

Fortunately, I have my original copy of my music collection to fall back on. But I was curious to see whether I could play these songs, from iTunes Match, on other devices. So I checked them on the iPhone 4S and iPod touch. And sure enough, they download and play just fine. So it's only the copies on the second PC that don't work. And deleting the local copies in iTunes and redownloading them doesn't fix anything; those file versions are broken too. Most curious.

It also doesn't help with the remaining ~100 songs that never found their way to Google Music. While I'll never really know why the Amazon uploader was able to find more songs than Google's, I would like to get the missing songs up to Google Music. And I have a few strategies for that.

First, I can use the web clients for each service to determine where things fall short. For example, comparing the genre view in each client, I can see that most of the discrepancy is in the Rock genre, which makes sense since most of the music I have is cataloged as rock. But that also doesn't help me find it or narrow things down much.

Amazon lists song counts next to the playlist names, which is great. But Google doesn't, so that seemed like a dead end until I realized I could get a song count in each playlist by opening the playlist. So that's a possibility.

Finally, I could use a Windows utility like Gladinet Cloud Desktop to connect to both the Amazon and Google cloud services and then compare the music sub-folders in each, side by side, in Windows Explorer. I may actually do that. (I've installed Gladinet to make sure this would work, and it will. This would also allow me to copy missing music to these services manually if I wished. Perhaps this is foddfer for a future article.)

Regardless of my own troubleshooting here, the important bit is that either of these services, Amazon Cloud Player and Google Music, can and should be used in tandem with iTunes Match to create cloud-based versions of your music collection. These can be viewed as offsite backups, I suppose, and of course both include background monitors that will upload new songs as they're added to your library. But they can also simply be used, and depending on what devices you're using, this can make a lot of sense.

Amazon and Google are both very Android-centric. So their services work well with PCs, of course, using the web clients, and with Android-based clients. These include Amazon MP3 for Cloud Player and Google Music for Google's service. If you use an Android-based device of any kind, you should be investigating both of these services.

Apple's iTunes Match seems like a natural fit for users of iPhones, iPod touches, and iPads. And it is. But I'd also argue that even those people who can't stand iTunes, and never intend to use it for anything, should still at least consider using iTunes Match at least once, in order to get a better quality version of their music collection. A collection they can then continue using happily on their PC, Android device, or whatever.

I'll continue using a mix of these products as well. I do manage my music collection with iTunes, because I use various Apple devices, including an iPad, an iPod touch, and an iPhone 4S. And while iTunes on Windows has some issues, I'll continue using it to play podcasts and iTunes U content on my PC, and to stream movies and TV shows to my Apple TV in the living room. Unfortunately, it won't be so easy for me to break free from iTunes.

And of course I'm a Windows Phone user. Currently, Windows Phone doesn't integrate with any of this stuff, Amazon Cloud Player, Google Music, or iTunes Match, so none of this is particularly useful there. That said, I don't use the phone that much for music consumption. I do subscribe to Zune Pass for testing purposes, and have configured the phone for that. And I do listen to podcasts occasionally, and to Spotify, on the phone. If you intend to use Windows Phone for media, you're going to have to stick with Microsoft's limited solutions for now, and/or with the few decent third party media apps (Spotify, Netflix) that are available on that platform. Hopefully, this improves.

Either Amazon Cloud Player or Google Music would be a fine way for you to listen to your own music collection at work, assuming the sites aren't blocked, and do so without having to cart around a device. You could simply listen to the music through a web browser. Both work very well in this regard. And taken to the logical extreme, truly forward-leaning folks might even consider using a cloud-based service as the "master" copy of their music collection, foregoing local storage all together. This won't work in offline situations, of course. But I could see some people doing it.

Accessing these services from the living room will require a bit of research. Apple users can use Apple TV to access iTunes Match-based music collections, of course. But if you store your music in Amazon's or Google's cloud services, your choices are limited or non-existent. Google TV does indeed have a Google Music app, and that will allow you to access your cloud-based collection via compatible devices. The trouble, of course, is that no such devices have sold well, and Google TV isn't exactly a common solution. I've not yet seen a way to access Amazon Cloud Player from the living room, short of loading the web client on a Media Center PC.

Microsoft's living room solution, of course, is the Xbox 360. And since that's about to change fairly dramatically, it's not worth dwelling on the current version's shortcomings in that capacity. I'll have a review next week about the major coming Dashboard update that should hopefully change that device's digital media prowess considerably. And heck, maybe someday Microsoft will surprise us all and offer truly deep integration between the 360, Windows Phone, and SkyDrive, and create a Windows-friendly alternative to these other offerings.

Until that fanciful future happens, today's cloud offerings--Amazon Cloud Player, Google Music, and Apple's new iTunes Match--all offer interesting options to digital music enthusiasts, and all work well with Windows. More intriguingly, perhaps, they can work together in interesting ways, too, and this is something I'll continue investigating. I'm particularly intrigued by the notion of managing my music collection in the cloud rather than on a single PC desktop. And with these services, that's become more possible than ever before.