Jacques, rather than getting into the complexities and possible inaccuracies of using those watt meter numbers and that amplifier efficiency figure, I'll analyse the needed power in the way I always do. First, as you point out, to play at the movie "reference level"(which I'd never do, being too loud for home use)requires a maximum output of 105dB per speaker channel and 115dB for the .1 LFE channel. For an M80 to hit a 105dB peak at a 7' listening distance requires the following power: the 91dB at 1 meter for 1 watt input sensitivity(anechoic)is reduced 3dB at 2 meters(using the reduction of level per doubling of distance in home rooms found in the work of Dr. Toole and others), 1 watt being needed for an 88dB level. 100 watts would produce a 20dB increase, i.e., 108dB, and the peak maximum of 105dB per channel would therefore require 50 watts.
Both my studies of audio technology and my personal experience indicate that this is the reality of the situation. Receivers rated anywhere in the 100 watt area have ample capacity for safe listening levels with speakers of average or better sensitivity, such as the Axioms.
Enjoy the music, not the equipment.