My build was a pair of Cabillas cups (PS1000 clones) with a Headphonelounge cable. I had the drivers mounted in the cups using a foam strip along the edge. I used an RSA Hornet with it for a while (the original version, not the M) and those are known for a tube-like sound. The result was a very neutral sound, that sounded flat, but when fed bass, went to immeasurable (sorry, a little hyperbole there) depths.
It might partly be your amp, and it might be your build. I believe you detailed this a while back, but how have you put yours together?
Wood cups from Martin (pretty big & heavy).
Xev cable from Zynsonix.
I've used blu-tac to push the drivers in a tight way to the cups. And the amp is little dot 2.
Edited by eyalcat - 6/5/13 at 7:46am