Some hope for ESI, maybe: https://kb.esi-audio.com/?goto=KB00337EN

If it's one of those and class compliant, you might be able to access all of it through alsamixer or one of the many frontends (maybe too many, maybe one for you): https://en.wikipedia.org/wiki/Alsamixer

The Audient situation appears to be a proper nightmare realm with non-class compliant stuff, but there is a tool with a list of caveats longer than you might want to deal with: https://github.com/TheOnlyJoey/MixiD

It's more best case scenario as an escape hatch and less problem solved, but it's something.

Well I'll test it when I have some time. ESI has a lot of routing flexibility on board, and I don't know how ALSA will present it to me, but I may report it here.

I didn't expect Audient to work, actually.