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

 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

charles1dad, the importance of doubling down depends on how linear the impedance plot of the speakers are to begin with, and how much power can be delivered once there. The OP 3.7's have an admirably flat impedance plot, so it's less of an issue here. Thiel's recommended power output would suggests about a minimum of 400 Watts into 2 Ohms. So the Aelius's measured 440 Watts is within that margin. Keep in mind the 3.7's have a sensitivity of roughly 85 dB/Watt at that impedance. 
 Sure it's valuable  to know what others have found to work for them, to try and get a consensus, but I have no idea who most of these strangers are, what there biases are, if they have any real experience, or have any idea if they know what there talking about.
 Some reports mirror my own findings, other report things I've heard, but have found that we have different priorities, other reports contradict my own experiences, others appear to be pushing an agenda without any true experience with the particulars at hand. I try and find a pattern from Audiogon posters to affix a personal value to their inputs.  Many different people choose various things for a myriad of reasons, not all of which make a lick of sense. I try to include those things that are objective and have proven themselves to most likely to be repeatable. Lots of factors? Yes, including these. As for opinions, well everyone has one, and so do I.