Here's another post I found relating to amping and how it's not just about volume.
Originally Posted by nickif
Below are the 2 headphones that I'm currently using. Th900s has been idling around for almost a year as I can't find an amp good enough to drive them. Phonitor was ok but unfortunately not too versatile thus I let it go; bha-1 was too warm and muscular but lack of a touch of delicacy, didn't stay longer than 3 months. I would say TH900s are among the most difficult to drive ( we are talking about quality rather than getting enough spl), GS-X MKII is the best I've heard with TH 900s, and it looks beautiful.
Yeah, again, it's either synergy (how the amp itself sounds, not the power), or improper comparisons between amps (which seems to be the case again).
Again, here's this thread explaining how the HD800 isn't that difficult to "drive," yet everyone claims it's picky with amps without doing any proper comparison tests between them. http://www.head-fi.org/t/724199/hd800-being-picky-with-amps-myth#post_10656025
The HD800 is bright by nature, by multiple objective measurements. Pairing it with a transparent amp and saying it sound bad because it's bright makes no sense whatsoever; that's how it's supposed to sound. Pair it with a warm amp and saying it sounds good is false because now you're just pairing it up with and EQ and you're no longer listening to how the HD800 is.
The TH900 is ridiculously easy to "drive" (it's like a portable headphone, 153 mW to reach 120 dB SPL at say 35-ohms), just that its sound signature is funky and certain amp pairings might have better synergy. It is a very coloured headphone in the first place.