Two possible reasons for alsa only allowing one application to provide sound at a time:
- The right alsa plugins are not installed (Void doesn’t include them by default)
- Hardware mixing is broken and ALSA failed to detect it.
Number 2 is not common these days, but I did have it on my previous (ARM-based) laptop. I don’t think you need anywhere as much code as people are quoting here, I got away with only this.
Number 1 bugged me for a while. IIRC I also needed the 32 bit versions of the alsa libs/plugins, otherwise Wine applications would take exclusive control of the audio.
These are the alsa-related packages I currently have installed:
alsa-plugins alsa-plugins-pulseaudio alsa-tools alsa-utils alsa-lib-32bit alsa-plugins-32bit