For what its worth, I previously owned a pair of Thiel 2.2 speakers (not the same as the 3.6, but still reportedly fairly difficult to drive). These were purchased on eBay mostly because the price was just too good to pass up as they were for "local" sale only - got them for about $300. At the time, I owned the following amps: ML 331.5 and a Krell FPB 200 (later replaced by a Krell FPB 300-C). I was able to listen to these speakers with all of the above amps (and others).
All were good amps with these speakers and allowed for excellent performance. The FPB 200 and the ML 331.5 were fairly close - the ML had a bit more neutrality while the Krell was a bit more forward. Both produced an excellent sound stage. FWIW, I was running a AA Capitole CD direct into both amps - so the sound was generally much warmer than either one of these amps would have normally sounded as a result. The FPB 300-C was a better match for these speakers in my opinion as it is a bit more neutral than the straight 200.
I used these speakers in a quasi nearfield setting and the imaging was superb. As a result of this little experiment, I fell in love with the Thiel speakers - though I no longer run them - now running Wilsons only. But I have always considered going back to the Thiels, the 3.6 would probably be my model - hence my interest in this forum.
I would think with the greater power of the 333.5, that the Krell 300 would be a more direct comparison or the 250 monos. I think that little extra bit of power over the 200 is helpful with the Thiels - or at least that was my experience.