The quality of songs ripped from CDs is entirely dependant on the software, hardware and settings you use when you rip it. The three main things that effect the quality are:

- the accuracy of the rip (exactly how close what is read from the CD is to what it should be)
- the quality of your MP3 encoder (some of them aren't as good as others)
- the bit rate you choose to encode the MP3 at (most people who are after decent quality would want at least a 192k bitrate)

One thing to be aware of, MP3s that sound fine played through a typical sound card in a PC can sound crap once you play them with a decent bit of kit like the empeg.