Thanks Lorspeaker, I hope so!
Krutsch- I know. It sounds a little nuts to me too, but since so many people say it, I have to respect it. So instead of just concluding that the 650s aren't what I'm looking for -- out of the box -- I'll do the break-in for a few days with continuous music and then make another evaluation.
I just read an article where they took measurements before and after 100 hours, and there aren't any real changes in frequency response. The main difference was in pad wear, which they say will affect the sound more than anything by making them more bassy.
I apologize if this is a tired subject for some of you. I'm chasing the holy grail of sound for my ears and I'm afraid its going to be Goldilocks syndrome: "These phones are too bright. These phones are too bassy..." For the reviewers that actually say there's a difference, the 600s sound like they may be what I'm looking for: not as sweet or flattering, but more natural, with less bass and a little more bite up top.
For me personally I find the 650s a little to dark and bassy and the hd800s are sometimes missing that touch of warmth that I like. The hd600 has pretty much a perfect balance for me, a touch on the warm side but it's a very natural sound, closest sounding to my speaker setup.