The amp is your decision, wait to see if the Denon works for you, if you think you want more then go ahead and get a seperate amp to drive the M80s, no harm in getting more power, whether or not you will use the extra power is up to you.

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