To the best of my knowledge, this isn’t something you can do at the system level. Individual apps can specify where they output, but not the system. You can control the volume of individual, active applications (i don’t know if it’s persistent). I imagine it would be possible to add that capability, but it would be via a new app or extension.
Thanks for providing that link. I knew about OSM, but didn’t fully grasp that (duh) it’s open which means I can help with the data. Time to get busy! :)