I found that changing the value for the address 121E5774 0000XXXX to a song not in your player may mute the background music everywhere else. I changed the value to a song I didn't have in the music player list, then I went into my house, tried selecting a new song in the list - which has no effect - and finally the background music was muted in all other places. I think it goes back to normal if you replace the value with FFF1 for nothing selected. When I did this with someone else in my house, I think it muted their background music too!