Amp upgrade for Thiel CS 3.7

^That is your subjective opinion. Not all would agree. While it's impossible to know for sure, I'll hazard a guess that Jim Thiel would have  stuck with his Krell power amp over the Gryphon integrated. Once again, it depends on the circumstances. One might be better than the other for some, and the other might be better than the other for some others. New is not necessarily better than old. There is also a price discrepancy that can't be ignored. 

There is no way old Krell design could compete with todays Gryphon gear in terms of sound quality.Gryphon was most likely not available in the US when Jim was still alive.At the time it was either Krell or Bryston you didn't have much choice for Thiel speakers.

Jim would have been blown away if the Antileon Evo existed at the time he was designing the 3.7s.

^There were others, and better than the Bryston’s too. Gryphon had a inconsistent presence in the US for a while, but I'm confident Jim knew what was going on globally. For the reasons mentioned above, I think Jim Thiel would have chosen the big Krell over the Antileon Evo(s) for the development of the Thiel 3.7’s.