Yep, 7eregrine is correct. I just did this and WAV from USB stick sounds exactly like it's coming from a CD, you end up with a huge 37MB song file but that's because it's not compressed, I used WavePad and literally took only about a minute to rip from CD to WAV format.
use any sound editor you prefer, I used WavePad:
pop into your laptop CD drive and load into WavePad
select the CD track you want ripped
CD track loaded, here you can do whatever you want cut, paste, gradual transistion in/out, etc, I just left it as original recording....
select save as and choose WAV format
choose the highest quality setting
what you end up with is a big WAV file, svae the WAV file to a USB stick and install the USB to the CX-5, the CX-5 will recognize the WAV file and enjoy. The sound QUALITY is EXCELLENT, same as a CD, it sounded like it's playing from a virtual CD player.