What about the HD650? Or is the O2 a poor match for those too? (not worried about sound sig at this stage, just ability to power)
I'm gonna be returning the 400s (if I can, or onselling them) if the sibilance doesn't screw off when I hook them up to the O2. At the moment, I'm *really* enjoying about 5% of the music I have and hating the other 95% (what I thought was a improvement was just the fact that I was listening to orchestral stuff rather than vocal-focussed stuff).
I really want to like these things, but my UM3Xs are just crapping all over them at the moment, s'yeah =/