Murphy, unfortunately i cannot directly compare your problem with the Onkyo 787 and the M80s however i can at least tell you about my setup and present experience.
My Onkyo 797 is normally hooked up to M60s but i have had a friend come over and test out his Kef's which are 4ohm rated. The 797 drives them without any problems and this is without having changed the setup options from 6ohm to 4ohm.
I really do believe that 787 should be up the challenge. But maybe it simply is not.


"Those who preach the myths of audio are ignorant of truth."