I bought these again today after returning my original pair a while ago after a lot of deliberation. Sadly, they seem to be immediately reminding me why I returned them the 1st time- fairly harsh treble lacking the refinement of the HD800 and sucked out lower mids giving it a weightless character and less (!) impact than both the HD800, and the HE500 I opted for instead of it the first time. I'm hoping burn in changes their character somewhat (although I don't believe in any significant burn-in changes) and gives them more body and warmth. I'm running them off the Matrix M-Stage which sounds good with both the HD800s and the HE-500s; both harder headphones to drive than the TH900s. I don't expect them to match the HD800s but at least be more enjoyable overall than the HE-500s, which are giving me that satisfying, tactile bass if not the full extension of the TH900s. When I had the Fostex last, I preferred the HD800s in a 6:4 ratio in overall music listening (for the HD800 vs the HE-500s its a 6.5 : 3.5 ratio) and at the moment its like 9:1 (if that) in favour of the HD800s.
Your problem IMO.