To my recollection, the solid state amps that have a reputation for sounding like tubes have been made by Pass and Carver. I'm sure there must be others too.
The Pass Aleph series was distinguished in this regard, although the most powerful one was the Aleph 1.2, which was rated at 200 watts, perhaps not enough for you. You might try out a used one, and it would be approximately the same vintage as the Thiel 3.6.
Carver made higher power solid state amps (like the M1.5t, M500t, etc), many of them deliberately designed to sound like specific tube amps of the time. These used amps are getting long in the tooth, although there are refurbishment/upgrade shops to keep them good. I am currently getting pretty good sound out of a Carver M500t driving Thiel 3.6s.
The Pass Aleph series was distinguished in this regard, although the most powerful one was the Aleph 1.2, which was rated at 200 watts, perhaps not enough for you. You might try out a used one, and it would be approximately the same vintage as the Thiel 3.6.
Carver made higher power solid state amps (like the M1.5t, M500t, etc), many of them deliberately designed to sound like specific tube amps of the time. These used amps are getting long in the tooth, although there are refurbishment/upgrade shops to keep them good. I am currently getting pretty good sound out of a Carver M500t driving Thiel 3.6s.