I would plug your Oppo into one of the TV's HDMI inputs and use the HDMI output from your TV to your Integrated. The TV will pass through any of the TV’s input’s digital signal to the out HDMI input in your amp. Then you can control your amp's volume with your TV's remote. This also lets the TV do the HDMI switching if you have more then one source.
I similarly use an apple 4k TV box into my TV’s HDMI input and run the HDMI out from the Tv to my Mac Preamp's E-Arc (HDMI) input. Now I can control everything from the Apple TV's remote.