Sound and vision did a bench test with this unit and found that it produced 320 watts per channel into a 4 ohm load with the impedance switch set to 6 ohms, not 8 or 4. With the switch set to 4 ohms the receiver only put out 55 watts, hence the reason why I would not want to buy this receiver if it had to run in this mode.

http://www.soundandvisionmag.com/receivers/2463/test-bench-onkyo-tx-sr875-av-receiver.html