Reciever for Martin Logan Source speakers-Two channel

I would take advantage of WiiM’s HDMI ARC input. Run HDMI from your TV into WiiM. That’s the only connection you need. Your TV has ARC HDMI correct?

You would then use YouTube app on your smart tv, or firestick, or appleTV to watch YouTube and the WiiM would play it. 
If oppo has YouTube app you are set to go as well. Oppo connects to your tv via hdmi, your tv back into wiim using arc HDMI output on tv into hdmi input on wiim. 

Thank you! I will try this setup when the WiiM arrives on July 14th.

The amp ultra comes in tonight. A week early. Look forward to getting it installed.