Converting iTunes purchases to AIFF

Hi guys, this is my first post here. I've got a quick question. I've read many of the comments already regarding audio codecs on this forum - great stuff, but I have an additional question that is probably simple.

BTW a little background --- I've transferred all my CD's to my hard drive in AIFF format. I've purchased a Carey Xciter DAC. I have a set of Focal CMS50 speakers and a Dynaudio 250mc Sub. And while it's not as sweet as my ol' living room tube system, it's nice.

Now here's my question. When you purchase music from iTunes it's delivered as a compressed file. After I purchase the music files I then convert the file to AIFF. What I'm wondering is this, does the fact that they were compressed to begin with compromise the music files? And if we start with a lesser file at the outset, changing it's format after the purchase seems like it would still be limited.

My concern is that if the files were stripped to cram them into a compressed format (so that Apple can sell them to the masses), I'd think that decompressing them on my computer would still reflect a loss of data.

Bottom line, does music purchased online from music resellers like iTunes (then converted to AIFF) have a negative impact on the music as compared to music that gets transferred directly from a CD directly (converted to AIFF)?

And while we're considering this question, if there isn't a loss in the compression and decompression process of iTunes music, what is the advantage to companies like HDTracks?

Any input you can give would be appreciated as I try to make sense of this. Thanks a bunch!