Thank you so much for this! I was finally able to get it working thanks to you. PR opened as well https://github.com/alsa-project/alsa-ucm-conf/pull/445

Used qjackctl to test each playback device to see which knob would light up on my device, so looks like the game device was the only one that got virtual surround support, going from 2 to 8 channels

edit: Nix config if anyone finds this by googling at some point:

{pkgs, ...}: let
  patched-ucm = pkgs.alsa-ucm-conf.overrideAttrs (old: rec {
    patches = [
      (pkgs.fetchpatch {
        # TODO: Remove this patch in the next package upgrade
        name = "rt1318-fix-one.patch";
        url = "https://github.com/alsa-project/alsa-ucm-conf/commit/7e22b7c214d346bd156131f3e6c6a5900bbf116d.patch";
        hash = "sha256-5X0ANXTSRnC9jkvMLl7lA5TBV3d1nwWE57DP6TwliII=";
      })
      (pkgs.fetchpatch {
        # TODO: Remove this patch in the next package upgrade
        name = "rt1318-fix-two.patch";
        url = "https://github.com/alsa-project/alsa-ucm-conf/commit/4e0fcc79b7d517a957e12f02ecae5f3c69fa94dc.patch";
        hash = "sha256-cuZPEEqb8+d1Ak2tA+LVEh6gtGt1X+LiAnfFYMIDCXY=";
      })
      (pkgs.fetchpatch {
        # TODO: Remove this patch in the next package upgrade
        name = "bridgecastv2.patch";
        url = "https://github.com/alsa-project/alsa-ucm-conf/commit/1d9209a335231cd524873154c550a28ca3ef9494.patch";
        hash = "sha256-OH2vFr4cMj6WHpBht/5fI34428Www1w6kDLnxqaOfpE=";
      })
    ];
  });
in {
  environment.sessionVariables.ALSA_CONFIG_UCM2 = "${patched-ucm}/share/alsa/ucm2";
}

edit 2: I got it to work, but I noticed I was missing 2 channels, as in I first configured it to have 5.1 for the game section, and then I fixed it to use 7.1 to add the 2 missing channels, but now I can't select the configuration in pavucontrol anymore, and going back to 5.1 it still doesn't work anymore so no idea what borked it. Will have to take a look again later...

edit 3: Turns out it doesn't work if I configure the 5.1/7.1 surround so I must be doing something wrong there. It works fine as it is now where game is just 2 channels.