I got it to work.
I used these steps instead:
http://www.pretendo.online/2017/01/25/adding-background-music-to-emulation-station/
Works great! You can easily edit stuff in the bgmusic.py file , like startsong and add missing emulators to mute the sound for.
I stuck my Pi in a Playstation 1 case, so my Pi-station is pretty much done now: