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

Thieliste, 
Michael Fremer reviewed the Aelius for Stereophile and when JA did the customary post review measurements this amplifier was stable at 2 ohms and produced 445 watts into that load.  I don't believe that your Thiels will be a problem at all. I just believe that it will be likely the best sounding amplifier of those on your list. Just my opinion. 
Charles 

 Charles1dad, As Thiel recommends a minimum of 100 Watts at 2.83 V/m the Aelius would seem to qualify as a suitable candidate, depending of course on desired volume out put and room size.  
  I think it worth noting that instead of doubling power into 2 Ohms from 4 Ohms as a true high current design would, or even increasing power (as spec'd) the afore mentioned Stereophile measurements show the Aelius dropped power, which incidentally would mean that it would be dropping power where the sensitivity of the speaker decreases. To be fair, it might be possible that power from the wall might have been sagging, but I doubt that explains such a degree of disparity. 

Thieliste, Some amplifiers halve their Class A output as they double down in impedance. Under powering a speaker, never lets the speaker perform optimally, increases distortion, and can potentially damage speaker drivers. Working and working well are different things.

Hello unsound, I'd think that one determines "working well" by how it preforms in the music signal chain i.e. reproducing music in your system.  You'd listen and decide if you like or dislike what you hear,  this is why a home audition is so valuable.  What we want from an audio product is for it to sound good enough to the point where we'd willingly purchase it. 

Too much emphasis on the doubling the power  as the speaker impedance is halved.  The Aelius can handle a 2 ohms load, the relevant factor is does it  or any amplifier "sound" good while doing so.?  You'll only determine that via one method, listening. Thieliste will fortunately soon have this opprotunity. 
Charles 

I’ve read numerous posts by Thiel owners who preferred tube rather than their SS amplifier due to superior sound quality in "their" opinion. These tube power amplifiers don’t increase power into diminishing loads, yet to many they managed to sound better. Lots of factors determine the ultimate sound quality we hear.
Charles