I used a 5 wpc SET tube amp to drive a pair of M3s. It was one of the best sounding systems I've ever listened to. M80s are as efficient as M3s though a more difficult load to drive.
I have a Kenwood KA 9100 2 channel integrated amp driving a pair of M22s (previously Dahlquist DQM 905s) in my garage system. The meters indicate that at decent listening levels the amp was rarely asked to put out more than 2-3 watts.
Of course, tube amps are known for soft clipping so low power tube amps are unlkely to hurt your M80s.
