I'm actually leaning towards picking up HD 650 and Nuforce HDP together in a few weeks. I've read a ton and can't really picture a better setup for the price based on my reading at least. I finally got a chance to audition HD 650 at a local head-fier's place and left pretty impressed.
Although it's very similar in sound signature to my Sennheiser IE8, I'm really craving the extra comfort, power, and soundstage of a full-size setup. One of the main things that attracts me about the Nuforce HDP is that it has an outstanding USB input section that can handle playing downloadable high resolution music from sites like HDTracks directly through my PC.
I'd be interested everyone's impressions on HD 650 and whatever amps you choose, especially HDP.
Thanks!
-Dave