Every component and cable is a little on the sharp side for a neutral/unforgiving speaker like thiel. First thing I would try - go to copper cables, I'm assuming yours are silver. Next, I would plug the amps directly into the wall and out of the chang pc. You will tame the tweeter some and get some body in the presentation.
This seems to me the most inexpensive way to possibly improve the sound and decide if you want to stick with Thiel. You almost need to build a system around Thiels - they will either punish you are greatly reward you.
I've always had a tube preamp in the chain and recommend that with Thiels. Next is a SS amp with alot of clean power like Mcintosh, Classe, or CJ...those are the only amps I have alot of experience with but they all work exceptionally well with thiel.
My final suggestion...don't give up on your Thiels.