So I just sold my ESP-950, and the reason was because I found an ESP-950 and Stax SRM-1/MKII combo here and had to give that a try.
I was very skeptical of claims of these "night and day" differences claims for the Stax amp before hand, and only dived into the purchase because I figured I can sell the Stax amp with just a little loss after I get to listen to it and make sure I am not missing much with the Koss E90 amp. That way, I can sleep easier at night, not worrying about missing out.
Boy was I wrong, and now I am in trouble. The Stax map makes an immediate and obvious difference to the sound, and now I am stuck with this purchase because there is no way in hell I am getting rid of it unless I can get my hands on a T2, BHSE or a KGSSHV for cheap.
The bass is much better controlled and extended. The highs are crisp, and the balance of the amp is just so much more than the E90. Don't get me wrong, the E90, considering that it came with the phones "for free", is a great piece of equipment because it allows us mere mortals to get into electrostats for a comparatively low cost (I know, they still go for around $700 out in the wild, but compared to other stats, they are cheap), but I feel the SRM-1/MKII just brought out all the good qualities of the phones that the E90 wasn't able to bring out. If you have the skills, go for a normal bias stax amp, and mod one of the plugs to pro bias. If you are like me, bite and bullet and get a stax amp, it makes such a big difference that even my tin ears can hear them immediately.
The other problem is that the Stax amp has both Pro and normal bias, which means that I am in BIGGER trouble because I will be looking for low end pro and normal bias Stax phones now.
Damn this hobby, and damn this forum.
Disclaimer: I only manage to find 30 minutes to listen to set up, with a DIYMod as source. I will look for better sources (I only have another iMod, which does sound better than the DIYMod, and a UD100) and try to really sit down and listen to the set up. I expect the difference between the SRM-1/MKII and the E90 to be even bigger with a better source.