Hmm, odd. I've had both Sony and Pioneer receivers, they both have offered an analog, multi-channel input selector (not a surround mode, but a dedicated input) that just passed the input to the output with only the volume control in between. I don't know how you'd tell yours to do that.

Pioneer PDP-5020FD, Marantz SR6011
Axiom M5HP, VP160HP, QS8
Sony PS4, surround backs
-Chris