I'm rocking the Gumby + Valhalla 2 --> HD650's right now. Sounds fantastic. I love the warmer, musical, smooth nature of the HD650's. I also have HD800's which I'll mod soon.
Would modding the HD650's (removal of foam and the coin mod) bring them closer to the sound of Anax modded HD800's? I enjoy having some different flavours in headphones, so I actually wouldn't want to try and turn the HD650's into lesser HD800's.
Essentially, I'm pretty happy with the HD650's as they are right now, except for wishing for a little more soundstage depth.