I've received the HE-400 today, and I would say that my first impressions were not as great as yours. Something was wrong with them. To my ears the mids seemed veiled compared to the rest of the spectra, I heard voices like behind a thin wall. They were here but not clear and had no impact (especially vs the HD650).
After few hours (burned-in the whole afternoon), this feeling went off and it's a relief to be honest. :)
Imo, quality wise, the HE-400 are on par with my D7000 (except the bass) and I find them better than the HD650 overall (maybe the HD650 are smoother and more fun-sounding). That's only my point of view after few hours of listening.
The details are amazing, I've recognised instruments in a song that I've not been aware off before... (too bad I didn't find a link on youtube.)
Oh, and I'm amping them with the Burson HA-160D.
I hope I will have time to do a better review, and It will be a good training for my English ! :).