Have 2 separate sound channel: background music and other (streamer mic, in-game sound, etc)
It would be awesome to have the choice to listen to your own music (as a watcher of the stream) while listening to the stream when the streamer puts its own music in the stream. If I were to do it now, there would be my music playing AND the streamer music playing which is just a mess of sounds.
Honestly sometimes I don't listen to a streamer just because I don't want to listen to the streamer music because either I don't like the music background or because I wanted to simultaneously watch something else with sounds on my end and I don't want listening to a mess of sounds (e.g. any other video or music, another stream, etc).
There could be 2 sound channels (1 for background and 1 for other sounds like streamer mic, in-game sounds, etc) with individual volume control (including mute option) handed over to the users. I would see those 2 volume control to be defaulted at equal volume, but at least we would have the option to mute one streamer's music when desired.
Thanks and regards,