Are you sure that the 805 is getting adequate ventilation? But now that I think of it, even if it wasn't getting adequate ventilation, it should shut itself down gracefully.

This link says "The 805 is a THX Ultra2 Certified powerhouse designed to drive mid to higher-end home theatres, with speaker impedances from 8 down to 4 ohms - a feat that only a truly powerful receiver is capable of. Its power is rated at 130 watts per channel.". I of course don't believe everything I read & hear but Onkyo seems to be pretty sure of itself.