I was unable to get music playing on the web build. Using latest firefox ESR and latest chromium I get am error:
Aborted('HEAPF32' was not exported. add it to EXPORTED_RUNTIME_METHODS (see the Emscripten FAQ))

Adding this flag to the build indeed fixes the audio issue in both browsers:
-sEXPORTED_RUNTIME_METHODS=['HEAPF32']

I'll make a PR for it I guess, but I have zero idea if this has any side effects. My game works fine and plays audio fine after adding.