Dan, welcome. First, forget about the Crown calculator. It has no relevance to use in reflective home listening rooms and grossly overestimates the power necessary for such use.
I calculate as follows: use 90dB as the 1 watt sensitivity for the M80 at 1 meter. 100 watts would result in a 110dB output at that distance. Since, as Dr. Toole and others have reported, sound level in a typical home listening room falls off(taking into account both direct sound and room reflections)about 3dB per doubling of distance, at a 10' listening location the 100 watts are used for about a 105dB listening level on brief split-second peaks. Typical receivers rated anywhere in the 100 watt area are ample. Relax and enjoy.
