Don't get too hung up on the various speaker wattage specs, the maximum wattage of a speaker is a guideline for damage, not much use other than that and the nominal impedance is only so meaningful compared to seeing the actual measurements across the frequency range. Speaker sensitivity tells you a lot more, use an spl calculator to see that relationship Peng mentioned with distance from the speakers and your desired levels The wattage of the sub's amp doesn't mean anything in relation to your question as the avr does not supply the power to the sub (unless you have a passive sub with no amp built in, then the receiver just won't work with that kind of sub, it would require an active/self-powered sub).
