I wish that I had an Oppo unit to try this, but that isn't the case.
I'd be tempted to set the SACD Priority (see item 6 on page 54) to Stereo, and run the Stereo Audio Outputs (item 2 on page 12) to the receiver. Then you won't need to fuss with it, unless you want the multi-channel tracks, which won't be a problem then as you'd be in the same room (I think), and it would be easy for you to make the necessary switch.
Generally speaking, stereo tracks on a SACD disc are still hi-rez.
"A stereo SACD recording can stream data at an uncompressed rate of 5.6 Mbit/s, four times the rate for Red Book CD stereo audio." - Wikipedia