I will be purchasing the Onkyo TX-NR807 receiver and I have written assurances from the reseller that it will drive 4ohm with no issues at all at reference levels for extended period of times. I told him I needed the receiver to play loud for more than 3 hours continuous without breaking a sweat.. he told me this receiver is fully capable of meeting my requirements.

Acoustic Zen Adagio, Veritas center, Axiom EP500, QS8s, Anthem AVM20, MC20,Adcom GFA7400