Why do you think you need a seperate amp? Why not use the Denon as a pre if you do get an amp? Also, you can run any combination of 4, 6, or 8ohm speakers at the same time, there is no setting or switch.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85