Use Xorg?
The viewers' experience might be all flashy and nice, but a lot of decently-capable rigs are an ugly mess on the control side. The operators like it that way, not because of the mess itself, but because it works, it's reliable, and they know where everything is 'cause they put it there.
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For audio though, I don't like to use OBS at all for that. Like pretty much all serious video production apps, any audio handling beyond a dumb passthrough is "token", and you should be grateful for what you do have. If you have anything beyond that "token", move the entire audio chain to an external thing to do all the work, and pass the final result from there as the only audio source at all, completely unchanged.
That external thing could be a physical console with a stereo USB line-in to feed the finished soundtrack to OBS, or a DAW to do the same thing but with a software connection instead of USB. Since you're on Linux, you might be able to install a very good, free DAW from the repositories:
On Debian and derivatives:
sudo apt install ardour
Once you've got that running and processing audio (use their forum for that), then you can ask about getting audio from there into OBS.
And here's another set of plugins that I like:
lsp-plug.in