i.e. Set the speaker impedance switch to 8 Ohms.

If you still hear distortion it more than likely means you've pushed the amps in the receiver too far and they are clipping--turn it down. The M80s can take peaks of 1000 Watts, they just don't like DC.

Pioneer PDP-5020FD, Marantz SR6011
Axiom M5HP, VP160HP, QS8
Sony PS4, surround backs
-Chris