I have the same combo. I run 5 electostats (martin logans) off 770. The longest/loudest I have used is at -4db (very loud) watched 2 movies. The amp was warm, I could touch back of the amp and not get burned. My speaker impedence varies from 5 ohm to 2 ohm.
I think its something in the amp, you may want to try with different set of speakers..

Just my 3 cents