I don't even think this would be difficult to implement. Twitch's VODs already automatically silence secondary audio streams, these could be exposed to the UI like the master slider already is.
This would also make it so the 3 unused audio channels actually have a use. The standard could be Channel 1 is game, 2 is mic, 3 is music, 4 is alerts, 5 is misc. And for simplicity, the master slider could just control all channels.
I don't even think this would be difficult to implement. Twitch's VODs already automatically silence secondary audio streams, these could be exposed to the UI like the master slider already is.
This would also make it so the 3 unused audio channels actually have a use. The standard could be Channel 1 is game, 2 is mic, 3 is music, 4 is alerts, 5 is misc. And for simplicity, the master slider could just control all channels.