You can't do it by changing the input? v1, v2, v3, and DVD?
I do it all the time with mine. I have the optical/coax sources assigned each selection. Like DVD player optical is DVD, cable box coax is v1, VCR is v2 (not a digital input, but if I had one, I can assign it.)
Onkyo has it set up on the assumption that you run both the video and audio through the receiver, but even if you just use it for audio, you can still select from the remote if you assign the selections a digital input.