PS Audio BHK 300 mono VS Modwright KWA 150SE mono VS D'agostino Classic stereo

I had Thiel 3.7s for a couple of years. From my firsthand experience, as I have posted here before, I would only recommend a high power high current amp for 3.7s.  I had the KW 150 and it simply ran out of steam and went into clipping even at medium volumes.  I would second the recommendation of BAT 600se and 655 Se as these amps really deliver a lot of current and give good dynamics.  I also had excellent results from Marantz MA9 monoblocks and a Krell Evo 402e. Jim Thiel used to demonstrate 3.7s with the 402e if that tells you anything. 

I completely agree that tubes should be in any system in which 3.7s are the loudspeaker.  I got great results with a tube preamp mated to a high current solid state amp.  With good source material such a setup performs at a level with systems costing more IMHO. With poor source material though 3.7s are an unforgiving mistress.