Thanks for the insight on the THS4031 vs. 4032 Filburt. Had I not gone to a discrete output stage, those were where I was going next, and my player's stock I/V was setup to use duals. Of course I knew if I went to these, I would have to do alot of rework/bypassing to the stock stage to begin with.
Regarding the NPO ceramics, are COG available in this size? I forget how big they get (0.1uf? or 0.01uf?) but it would be interesting to see if you noted similar problems with these.