I have been in and out of this thread for many months, attempting to alleviate the dilemma of deciding to add the TH900 to my headphone collection, as a way to complement my HD800.
A few weeks ago I bought the JVC SZ2000; I amped and eq'ed the heck out of it. The bass was monstrous and unexpected. However, the only enjoyable part was the tremble-inducing bass. Everything else about the headphone's sound was poor, thus, the overall experience was unenjoyable, unless I was completely focused on the bass.
So today I bought the TH900, which will arrive tomorrow. I will eventually post my impressions, and see how these headphones stand, especially to people who are in the same dilemma I was in.