The HDMI Forum, responsible for the HDMI specification, continues to stonewall open source. Valve’s Steam Machine theoretically supports HDMI 2.1, but the mini-PC is software-limited to HDMI 2.0. As a result, more than 60 frames per second at 4K resolution are only possible with limitations.
I know that there are some complicated configurations that you could use to get the audio feed from display port to your receiver, like running it through a splitter that will strip out the audio and send it to your receiver separately. I’m pretty sure there are no mainstream AV receivers that will do what you want because the market is split between home theatre and PC, as mentioned elsewhere in this thread, and manufacturers need to be convinced there’s a market for it.
In that situation, I would connect the output device, in this case a PC, directly to the TV/monitor with DP, and run optical audio from either the TV or the output device to receiver.
You lose some of the integrated control that HDMI-CEC gives you, so get a good universal remote that can adapt to this set up and get one-button source switching back.
I’ve considered this - I would like multiple sources on my receiver though, so this as you say requires at least a universal or 2 remotes to swap back to the reciever. My projector (current one) only has 2 HDMI Ports. Perhaps in the future this can be my setup.
I run a USB DAC off my pc, then have RCA cables going to my speakers. Usually the DAC built in to a PC or TV is terrible compared to a dedicated one