See, I told you that you didn't need all that power! Okay, I was looking for something in the area of 20 volts peak. The suggestion of maybe using a test tone disc at a specific frequency(a few hundred Hz, say)rather than music is a good one. Then the frequency and the level won't vary(except when you vary it), and the specific M80 impedance at that frequency(from the NRC measurements)can be used and should be adequate.

Enjoy the music, not the equipment.