They are 4 ohm nominal speakers and a load for any AVR to drive. The 805 is supposed to be 4 ohm stable. Whether it can handle your setup without choking only you can answer. If you are asking about a setting on the AVR, switchable from 8 ohms to 4 ohms...I'd leave it in 8 ohm mode. Those switches actually limit current to protect the AVR, but your speakers need all that current. Personally, I'd at least get a 2 channel amp on the 15s, they'll improve and it will take a ton of burden off the AVR, YMMV.