Any half-way decent modern day aftermarket indash cd player can handle your stock 8 speakers. That salesguy's an idiot (sorry but true).
You can make an aftermarket player sound even FAR better by adding an amp, sub amp and subwoofer, then replace the speakers with better speakers but most people probably won't want to do all that themselves.
I do stuff like that with all my cars as that's the only time I really listen to cds (and now XM radio too, a great option btw). I do it myself but it can take time and patience to get it perfect (not including $$$) but to me, it's worth it as once done, it'll sound better than ANY home system.
The best place to get good deals on auto stereo players, etc is via retailers on Ebay. Once you find what you want at a place like Best Buy, Circuit City or Crutchfield, do a search on the same thing at Ebay and you'll be amazed. Just buy from a retailer with good ratings to be safe.
If you'ld rather not install it yourself, any car audio place like BB, etc can do that too.