Apparently we still cannot have multiple AudioListeners in a scene. 
What are my options to enable multiple audio source mixing for a 4-way splitscreen 1st/3rd person game?
I know FMOD can handle this.
But perhaps there are other, preferably open source audio engines or even workarounds? I learned about virtual listeners where you wrap all audio sources but that idea is 15 years old and probably kills performance. Any alternatives?