If you have a good quality D/A converter (24 bit burr brown) in your CD player and are running an external amp......you will be hard pressed to hear the SQ difference. I am running a $130 Kenwood deck with a 24-bit Burr Brown into a Rockford 501x amp....it sounds great to me, and I've heard 100's of systems. I think its more like 50% install and 50% equipment...contrary to what I read on this forum.
Current head units:
Kenwood, Pioneer (x2), Harmon Kardon.... all in near daily use.