<font color='#000000'>Hi Vanillavato,
Audio CD's are recorded with a bit depth of 16-bits, and a sampling rate of 44,100 samples per second. That's four bytes per stereo sample, times 44,100 samples per second, or 176,400 bytes per second (that's 172 kbps in computer lingo, or 176 kbps in any other field).
MP3 audio uses data compression to reduce the digital bandwith. Since it is a lossy compression, it can have audible side effects. Critical factors include the compression ratio selected (128k is better than 64k, for example), and the material being compressed. I have yet to see an MP3 compressor that could do a credable job with recordings of Harpsichord music (as just one example of where MP3 can get into trouble).
Personally, I would not use MP3 files to evaluate equipment. On the other hand, I don't use MP3 for much of anything. If your primary goal is to listen to MP3 files, then it just might make sense to evaluate gear using the same kind of material you plan to listen to most of the time.
If you want the most from MP3, try to find an encoder that handles VBR (variable bit-rate) encoding. Depending on the encoder, this can be an improvement over fixed data-rate compression.
My advice would be to audition gear with the same kind of material you expect to listen to most of the time once you get the gear home.
Hope this helps,
Chuck</font>