Like you, I have owned a pair of Thiel 3.6 since 1995. I traded a pair of Thiel 2 2
to get 3.6s
from Soundings, Denver, Colorado . I have used several amps to drive these including PS Audio 200CX, Audio Research 100.2, and Krell KST 100.
Only after I got Mark Levinson 23.5, Thiels came to life. Other amps were not bad, but 23.5 takes this to whole another level. So my recommendation is to track down a ML 23.5. Since you are used to tube sound, ML 23.5 will give a very similar presentation, but plenty of wham when needed.
Rest of your system is top notched and should give you many hours of fun. I understand ML 23.5 is "old" technology and difficult to service if needed. But they mate very well with Theils unlike many other amps. If you have money, then you may as well track down a pair of ML mono blocks and that would be even better.