How about a unit that connects to your normal head unit using the CD-changer conection (Phatnoise-style), and can be controlled via the normal CD-DJ controls. Easy to fit with standard cables. Make it rip CDs internally, and use speech to give the user feedback to make up for the lack of flexibility afforded by the usual CD-changer controls. That should attract the mass market appeal (i.e. no talk of PCs, synching, MP3s or other phrases that scare the mass consumer), which should get the sales volumes up . Sell it to them as "just feed it all your CDs and then choose what you want to listen to".

Ensure it can still connect to a PC for those that want it (wired or wireless) and hope that you've come up with the right feature mix!!

Nick