No, OBS's audio is just that bad. If you set it to stereo, then you either get the first two channels, or it insists on downmixing the entire device as if it were surround, to stereo, and THEN it lets you play with that downmixed mess. It only so happens that the first two channels of surround sound are the front corners, so if that's all you have, then it kinda works anyway.
The back corners and sides, whatever channels those are, mix with the front corners at a lower level. The center channel goes to both sides, and the subwoofer disappears.
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If you already have a DAW, just use that, and move all of your audio work over there. Don't do any of it in OBS. Keep OBS silent, except for a dumb passthrough of the final finished soundtrack as provided by the DAW, as OBS's only audio source at all.
Videos, and other soundtracks that can't be moved out of OBS easily, go to OBS's Monitor only, not the stream or recording, for the DAW to pick up. And don't Monitor the DAW's return to OBS, as that would create a feedback loop.
The DAW also feeds everything else, like your speakers, headphones, other apps, etc. OBS doesn't do that anymore either, in your rig.
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If you must use OBS, and not the DAW, you can try the ASIO plugin. It's supposed to allow you to choose channels from a device, but I've also seen reports that it doesn't work with the current version of OBS. Might be worth a shot anyway, but I'd seriously look at using the DAW instead, because OBS has more audio problems than just that.
