Another question our readers asked was what happens if your library is filled with higher quality rips, such as tracks encoded in Apple Lossless (ALAC) format. Matched tracks will still be in 256Kbps iTunes Plus format, while uploaded tracks will retain their original format. Tracks aren't replaced in either your iTunes library or on your devices unless you request them to be, so the lossless files in your main iTunes library will be safe. Sticklers might balk that matched tracks won't be available via iCloud in a higher-quality format, but if you don't require lossless quality on your mobile device, having access to smaller 256kbps AAC files via iCloud may be a benefit.

Unless... Okay if iTunes does allow you to find/replace everything in your library with what they have on their server (and not just pick out individual tracks), you'd be stuck with AAC files, but only temporarily. If you change the import settings in iTunes to use an mp3 rather than AAC encoder, a menu option appears that allows you to convert any track in your library to mp3. You could just select your entire library, hit "create mp3 version", and go to bed. Dunno if it's worth it or not, especially considering they want $25 for iTunes Match, but it's the only option I could think of that didn't involve re-ripping on your part.