Is powerfull Amps only for low sensitivity speakes?

It is true that distortion goes up a little bit at lower levels, but it is still very low and below the noise level: 0.05% at 100 mW. Look at graph 16 in particular, for the output range of 480mW to 7.7 W rms. In that range it never gets above 0.015% and rapidly descends to 0.01%. There is no way you can hear this.

Sure you can- if you have high sensitivity loudspeakers!

What you are not taking into account is the nature of the distortion (mostly higher ordered harmonics) and the fact that the human ear uses the higher ordered harmonics to sense sound pressure. We are more sensitive to them than almost anything else! So they manifest in amounts this small as brightness. This is what has fueled the tubes/transistor debate for decades.

But a powerful solid state amplifier allows you to use mostly far better inefficient speakers and avoid the distortion and non-flat frequency response of many tube amplifiers. Anyway, we are not going to persuade each other.

williemj"But a powerful solid state amplifier allows you to use mostly far better inefficient speakers and avoid the distortion and non-flat frequency response of many tube amplifier
I am very sorry you seem to be substantially misinformed on this basic principal there is no defined and verifiable factual correlation between speaker efficiency and speaker quality there are outstanding examples of each general type of speaker system of course you may prefer inefficient speakers in your Music Reproduction System to satisfy your own biases and that of course is completely fine but to claim that it is for inherent advantages of said inefficient speakers is mistaken, misleading, and a misrepresentation of clearly established fact. 

Clearthink would you please do something about your grammar? It might just add some clarity.

williemj"Clearthink would you please do something about your grammar? It might just add some clarity"

Well williemj I thought this was an audio group not a grammar group but since your raise dthis matter why don’t you issue me clear instructions on precisely how you would like my language to correspond to your considered ideal of how people here should communicate in the forum. Go ahead I’ll listen and take notes because obviously you have superior intellect on all things and not just audio but also now grammar. Of course it is patently clear that you are grossly mistaken about the inherent superiority of speakers of high efficiency and so I rather assume you now take issue with grammar and I suppose once this issue with grammar is resolved to your complete comfort and satisfaction you'll then raise another completley irrelevant issue such as the proper way I should brush my teeth or tie my shoes.