Unable to send multichannel PCM audio from PC to LG B6

[uKER]

I recently purchased a B6, and came to realize my good old AVR (a Denon 1612), featuring HDMI 1.4, won't do HDR pass-through, so intending to keep the Denon, I switched to having the TV in the middle, instead of the AVR as I did until today.  I have managed to get audio sent from the TV to the AVR via both ARC and optical, multichannel working fine, but the problem came when I tried to have multichannel audio from the PC to the TV.

The problem is, the PC (using a GeForce 1070) sees the TV as accepting only stereo PCM audio, and only allows to select stereo in the device's speaker setup. Needless to say, I need 5.1 PCM to get multichannel audio in PC games.

I even tried using an EDID override, copying the audio capabilities from the Denon to the TV, which allowed me to have Windows think it can send the TV any of the stuff the Denon takes, but even then any audio from channels other than left front and right front  is lost along the way to the AVR. My guess is that for whatever reason, the TV is decoding the stream and only letting L and R through.

On the bright side of things, multichannel pass-through does works fine for DD and DTS streams, allowing to watch a movie on the PC and have semi-decent multichannel on the AVR. Dolby TrueHD and DTS HD, though, are a no go, even using ARC (optical obviously doesn't support HD audio).

So yeah... Any ideas? Suggestions?

I'd like to think I won't be forced to buy a new AVR just to have it pass through HDR, so any help will be appreciated.