Recommendations for used CD player


I'm looking to improve my sound by adding a CD player to my system.  I'm currently now just using a Yamaha DVD player along with a Yamaha Aventage home theater receiver (which uses ESS Technology ES9006 SABRE DACs).  I use the receiver as a pre/pro with a Threshold S500/II amp and B&W 802 Series 2 speakers.

Right now I really like my sound and I've read these DACs are fairly high quality, but wasn't sure if I could get improved sound by adding a used, higher end CD player and possibly outboard DAC.

No SACD needed, my budget is about $400-500.

Thanks.

dastro
Honestly, I don't think anything for $500 is going to be better than what you have now.  Maybe stretch to a grand and buy a used Cambridge 840c or something like that.  I happen to think the Cambridge players are very good for the money.  
I just purchased a new Cambridge CXC Redbook CD transport for a headphone system new for $400.00 and am very satisfied with it check these out for a new solution as apposed to used.
To improve the sound I would look into an external dac and a low cost cd player for a digital transport.  To complement your ESS dacs, look for something that has Burr Brown or AKM dacs that way you can have a variety because each has their own sound signature.