I owned the 3.6 many years ago. They need "current". I tried Krell KSA 100, Classe CA-150, and VTL 225 monoblocks with the 3.6. They were fine. However VTL 225 could not control the bass as good as the other two SS amps. A good case in point is when I recently auditioned a 180 wpc high quality tube mono amps with the Revel Salon 2, the bass was not there. It is the current that counts.
When I got the Brown Electronic Lab (BEL) MKIII monoblocks, the sound of the 3.6 became spectacular. I used tube pre to introduce some tube characters into the sound though. I was using CAT SL-1 Signature. Unfortunately, BEL is not around anymore. You can only buy used and they are very rare.
I recommend good SS amps (at least 100wpc but 200wpc or more is better) that can dive deep to 2 ohm with the 3.6 and also a good tube preamp. If you really want to use tube amp, I suggest you try it home to make sure it can work with the Thiel. For SS amp, I think the Parasound JC-1 monos could be a good candidate.