Amp experience

Unfortunately ratios aren't how logarithmic scales work and it's deceptive to frame the explanation in such a way. 

I typically listen at an average power level less than 3 watts. That gets me up into the 85-90dB region at my chair pretty easily. 6dB is perceived as a doubling in volume. The 60 watt class A envelope allows for 13dB of headroom beyond that. It'll drive 120 watts in class AB, but that doubling of power is only buying another 3dB. 400 watts? That's over 111dB. That's extremely loud even for transient peaks. That will damage hearing quickly. I personally have no desire to own an amp with that capability. It's pointless, but beyond that, it's becomes more technically challenging to build an amp that performs excellently at both 2 watts and 400. I'd much rather have 2 or 3 truly excellent watts than 400 dangerous, very seldom uses watts. But, if you're using very inefficient speakers with ugly impedance characteristics, you'll need that kind of power. Maybe more. 

kosst_amojan - I know how logs work, what I don't know is whether ktz03110 does.   Consider this, the 10*log(10) of 20 is 13 dB, 10*log(10) of 200 is 23 dB.   That an increase of 10:1 in power. 

Another way to look at it is if music is running 20W at one point in time and the next point in time music demands 200W, that is still a 10:1 change in power that the amplifier has to produce. I purposely used those numbers so I could say a 10:1 power change.  I never said a 180 Watts is 10dB. 

If I had a sound system that only used 1W typical, I wouldn't be looking at a 200W amp, as I mentioned above, as well as the reasons you stated.

My point was that very few people use anything like 20 watts. Average volume at average distance from average sensitivity speakers required more like 2 or 3 watts. I honestly don't know why people think they need 400+ watts unless they're driving very difficult speakers and/or filling a huge volume of space. 

Or listening to Classical music .

Yeah..... That's the typical claim.... Like nothing else even comes close..... Which is demonstable false.