Justin

Besides the way you transport the audio data the problem is in the origin; .mp3 format or similar always cut off data that is neened for giving you the best of the recorded album.

So, the best way is to use an original cd of course or give it a go and test some formats.

Please, do see, the following link:

http://www.cdburner.ca/digital-audio-formats-article/digital-audio-comparison.htm

HTH.
 

@Beology

If you're thinking of buying BL5s and using a Mac as a source, then here's what I'd suggest:

1) Your harddisk can store your CDs in the original format (just buy a large HD and connect it to your Mac. There are also computer independent servers that you can control without needing to have a Mac connected, but let's go with the Mac for now). You can also use the HD in your Mac, but if you're building a large library of uncompressed files, then you'll eventually want an independent server.

ADDING: Sometimes I'll play a CD from the Mac, but that tends to be noisy, so the Mac has to be in another room than the one I'm listening in. That's no problem with the Airport Express, though. I control the Mac through the WiFi.

2) The Mac will send the digital signal, uncompressed, to your Airport Express (AE). You may be aware of this, but the AE can deliver both an analog signal to the minijack connection and a TOSLINK optical digital out through the same minijack. (Requires a TOSLINK minijack connector).

3) Get a TOSLINK to S/PDIF converter. (There are various available, from cheap ones to pro-grade. Get a reliable one within your budget).
Connect your AE to the converter through the TOSLINK optical cable.
Sample converters: