But if the idea is to bypass the AVR, that is irrelevant.Yes, but not only: if you find an AVR that accept more than 8 channels (PCM) by HDMI (it would be absolutely possibile, as per HDMI 2.0b and 2.1 specs), you win a Caraibic holiday...
Why would Windows have this limitation? How do these multichannel audio interfaces work then, that have more than 8 channels? Something like Behringer UMC1820 has 20 outputs. Basically, al DAWs have no issues with this.