I listened to the 640C (with a 640A) this weekend and, maybe I had too high of an expectation for it, but it didn't exactly blow me away. I have to say it was in a less than optimum listening environment too, so I may have to give it a second shot, and maybe ask them to set me up in an actual listening area instead of their display. I'm definitely not saying it isn't a good player, it is. The sound was smooth and natural sounding, bass was clean and vocals were clear.
Any reason not to consider the Arcam CD73? I've heard this guy and was pleasantly surprised. IMO, it sounded better than the 640C.
I haven't heard the Rotel or the NAD, but I've always been a fan of NAD.