Brian, the relative volume control settings can be pretty meaningless as to the actual speaker volume(and required amplifier power). For example, what if a ppp musical passage or someone whispering in a movie happened to be the source material at a particular moment. Even if the receiver was turned up to the +18 max, maybe only a watt or two of power would be used, even listening to that material at a level much louder(maybe mid 80s dB sound level)than the producers intended.
The actual sound levels have to be measured with a separate SPL meter, such as the RadioShack unit, and what you should be concerned about is neither the receivers nor the speakers, but your hearing. When I'm listening at a "loud" level, typically this is an average level in the mid 80s of decibels, using about 1 watt. In my most dynamic classical source material, split-second peaks might be as much as 20dB higher, requiring about 100 watts. More commonly, I'd listen at levels about 10dB lower than this. Again, pushing your 2310 or M22s too hard shouldn't be the concern; they can take more than your hearing can without permanent damage.
