Reviving this thread again since I'm jumping back and forth between here and HF, and I'll likely get some more brutally honest opinions about amplification here on the TH900s vs conjecture and hypotheses over there.

Finally got my PWDII back and hooked up to the X-CAN V3 that I was previously connecting directly to PC to burn in the TH900s a bit. Things definitely opened up a lot more, a bit more detail & spatial (ie. sounds more opened up than closed in) portrayal and further dialing in on top and bottom end extension at the frequency extremes. Glad to have my PWDII back (2.02 firmware).

I do get the sense that the X-CAN V3 (with X-PSU V3) is providing a more "bloated" picture, and hence making some types of music sound more "slower" than it should be, namely with electronic music. It's also a darker sounding amp with its tube stage in the circuit.

So, looking at some sub $1K options to essentially drive these headphones. May stretch a little over if need be but wondering what have you guys actually LISTENED to which gives me a little more neutrality than what I have via the amps. Of course, I'm well aware that the TH900s are colored so no need to emphasize this point. I believe that the colored nature of the headphones themselves is what I want to preserve. I just need something on the amplification side which doesn't further color the headphone's signature.

Thanks in advance.

If you want more neutrality, I'd EQ them.  No change in amplification is going to have as large a difference in colored/neutral as its so darn boosted in the low end.

Thanks for the tip, Tari. Guess what I'm asking for is about changing the subtle shade of grey to be lighter than darker. 

I've read purrin's review on this. EQ is an option but something I'd rather not fiddle with if I'm playing CDs through a transport directly into the PWDII as well. Not sure about PWD filter options, which I haven't played around with yet.

Also, some of my music listening will be through streaming services, such as MOG. Are there any EQ applications which sit between the streaming app and the output?

Need to try figure out my ears some time. Using sinegen, I hear treble peaks pretty much at 5KHz and 10KHz. Doesn't quite match FR graphs from anywhere I have searched. Anyone else?

http://en.goldenears.net/17034
www.innerfidelity.com/images/FostexTH900.pdf
http://personalaudio.ru/raa/otchety/naushniki/fostex-th-900/

Need to try figure out my ears some time. Using sinegen, I hear treble peaks pretty much at 5KHz and 10KHz. Doesn't quite match FR graphs from anywhere I have searched. Anyone else?

The 5 KHz peak seems to appear in measurements that use a simulated ear. There's always a narrow peak between 9-10 KHz with any headphones for me, it's due to my ear.