ATC SCM40

No offense intended. 

@steve59 To be honest, I didn’t even understand your point. 

ATC tends to suck power like there is no tomorrow. I used Nilai class D to power my ATC, and it sounds pretty good. Class A or tube is suboptimal for these speakers. These amps are just not having enough damping factor.

@viethluu -glad you own ATC, but if you consider having a wide dynamic capability "sucking power" I guess you could say that?  Most of them will play a good deal louder at lower distortion than other speakers of similar size (which is what makes them work in studios).  Also I am compelled to add its amps that have a "dampening factor", not speakers.  You are right that dampening factor is indeed an issue!  Dampening factor is best understood as how much "control" the amp has over the drivers, revealing itself on low frequency drivers in audible demos between a higher gauge cable vs a lower gauge one.  It's a pretty easy demo to do at home.  Compare the same length in two different gauge cables and you will likely hear the difference in tightness of bass.

About Class A.....you are right that it is suboptimal for moderate efficiency passive speakers unless you listen at low levels.  Class A doesn't quite have the appeal of Class AB anymore due to high heat at higher power output levels.  Its expensive, it runs hot and most of us don't want noisy ventilation fans on our amps in our living room.  Class A is not easy to design/build at high power levels (such as 100/ch)- so they are more likely to be found very low power outputs-  such as 5W to 25W per channel.  

Brad