That's 140 x7 into 8ohms but the 4 ohm load increases the output by about 45%, you are running about 240Watts into the M80s and the 4308 was never designed to run that much power out. This is why we are suggesting the seperate amps, at least for the M80s.

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