Just out of curiosity, let's say he did turn his 50W receiver all the way up, and fed the M80s a square wave. I know square waves have a lot more power than an unclipped sine wave, but given that the M80s can take a rated 400 watts, and 1200 watts is unofficially the point at which the drivers blow, could a 50W amplifier really damage the M80s? I mean, If I can feed the M80s a 400W sine wave at 10KHz, why not a "50W" square wave? (50W in quotes because I'm not sure how to figure out how many actual watts the speaker would see)
My guess is either the crossover or tweeters would overheat, if anything.