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 have never seen such excellent feedback/advice from so many on any one thread. thieliste, I think that your audition of the Ypsilon will tell you a lot.

I am totally delighted with a Classe' Audio DR-9 (100W/ch@8 ohms rated high current SS amp that doubles down to 2 ohms) with my "older" Thiel CS5is using a MW5400ES tubed player for the front end. The lower-rated-power DR-9 simply does more things right than my Krell FPB-600c at all but insane volume. May be the same with the Ypsilon vs the D'agostino or Krell in your system, dunno. Only your ears will know for sure.

Recent experience has taught me that tubes somewhere in the chain are magical with the Thiels. Makes them relax just the right amount to bring out the musicality vs analytical over-achievement without.  

As always, the synergy of the equipment chain makes the difference.
emailists' advice to leave a good amount of your budget for cables, cords, and a top power conditioner is prudent, IME.

Best to you thieliste,
Dave

dlcockrum i'm surprised you're able to drive the most difficult Thiel ever with only 100 watts even if it's doubling.
I'm sure the D'agostino classic would be a perfect match for my CS 3.7 with let's say a VAC or VTL preamp.
But who knows perhaps the Ypsilon Aelius will have enough current and sound beautiful on the 3.7s.

"dlcockrum i’m surprised you’re able to drive the most difficult Thiel ever with only 100 watts even if it’s doubling."

Quote from ’Blazing Saddles’: "It’s twue! It’s twue!" lol

Over 25 years with several different amplifiers driving the 5i’s (including one of the highest-wattage monsters of all time), I find that it is much more about current delivery and superior amplifier design (minimizing anomalies at the frequency extremes, the ability to reproduce correct timbre and deliver micro and macro dynamics optimally) than rated power (to a limit).

Enjoy this golden time in your audio journey, thieliste.

Dave

Thiel recommended between 100-400 Watts for the CS5's. In my conversations with JIm Thiel he told me his all power recommendations were based upon quality ss amps that could double down, and that should one choose to use tubes, etc., they should increase the power  accordingly.