And just switch it off of the HDMI to the 707 when playing music.

Why do you need a way to de-activate an unused output? You can connect the HDMI and the analog outputs to different logical AVR inputs and use the AVR's input selector to choose which one to use. Also, on many AVRs, you can connect them to the same logical input and use a button on the remote to choose.

Kal

Just go to the Oppo set up menu and turn off the hdmi audio and keep the video.

I think every Onkyo for the last 5 or 10 years digitizes the analog signals anyway for use in thier DSP modes.  Even bypass is just flat DSP sent back to the DAC for amplification.

I'd be surprised if the Onkyo DAC from HDMI isn't a higher fidelity than the Oppo anyway.  I know it's a little against the grain on Stereophile to not sing the praises of Oppo ad-infinitum, but Onkyo didn't just start making audio equipment yesterday, and they are actually very good at it, thank you.  If you crack open an Onkyo device, even an inexpensive one, you'd be amazed at the quality of active devices.

Best if luck.