No difference really, just the outside finish (if it were aluminum), model number and a different CD mechanism. It will work just the same.

Early (most?) 5500's do not have the tray cutout for CD singles, so if you need to play those, a 6500 will be a better choice.

Of all the CD5500s I've come across (quite a few!), the vast majority have been the later ones which can play the CD singles.

Cheers

Nigel 

It turned out, this CD6500 is WITHOUT the RCA- only DIN!

On my BM5500 and CD50 I've made the controls via DIN and sound- through RCA, which gives freedom to use any RCA cable to adjust sound to the speakers and room.

Are all CD6500 lack RCA and I'll better look for CD5500 instead?

Thanks!

Well, I'm not going to get into the cable debate... But I'd just use the DIN instead of getting my choices limited because of a connector.

6500 indeed has no RCA connectors, I forgot about that.