What I did feel, however, is a recess in the mids, especially in the vocals range which make it sound more "heavy" . By comparison, the HE-500s do sound more open and fuller in this area. The 400s don't quite have the magic mids of the 500s.
The treble quantity is a bit more that adequate for me (I'm used to the smooth treble of the 500s), I hope it will tame up a bit with burn-in.
I noticed the same thing and just returned my HE400's, I listen primarily to rock and noticed during several songs that the vocals in the track seemed to be recessed while the high hat was overpowering. I think turning them up to hear the vocals caused the highs to give me tinnitus which I now have and won't go away. I've never had tinnitus from a hp before and don't listen at excessive volumes. I would love to see a real frequency graph to get a visual on what I am hearing to confirm it. I bought some HD600's based on a recommendation and to my ears they have better balance across the frequency spectrum. Interestingly I play bass guitar and I feel that the HD600 more accurately portrays what I hear coming out of my bass amp than the HE400 but then again I'm not a dubstep or hip hop guy and am not fond of synth bass. I had rev. 2's btw.