The fact that the system works for awhile and then failures start certainly suggests some sort of power issue either through the receiver or the receiver itself, ie clipping. I would be trying a good surge suppressor like Panamax, Belkin or similar for starters. Also if possible try running the system with a known good avr perhaps borrowed from a friend.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70