Fred, just to comment and hopefully not be too pedantic on that point, use 88dB for the 1 watt/1 meter M80 sensitivity. Then at 10 feet(using a typical 3dB loss per doubling of distance in a reverberant listening room), 1 watt would give about a 83dB sound level(per speaker). 1/10th of a watt would give 73dB and 70dB would require about 1/20th of a watt. Headroom isn't relevant to the power actually in use at the specified level and distance.

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Enjoy the music, not the equipment.