Any speaker rated at 4 ohms and 85dB definitely needs their own separate power amps. No way, no how should a surround sound receiver be trying to drive pigs like that. That goes for NAD, Rotel, B&K, Marantz, etc... There's not enough room in a 7.1 surround receiver for massive toroidal transformers and huge heat sinks. The 5800 series receivers from Denon are outstanding units, but IMO would perform much better as a pre amp in that situation. (exception - 5805 and a few other flagships, but I still like a separate power amp with pigs).
Try using the amp to drive the speakers by itself, then experiment with biamping. I'd use the NAD amp to drive the bass when you biamp. The mids and highs won't require that much power and can run off the 5800.