To be 100% precise I am using only one System and in X session 1 I login as user1 to do more regular stuff like hearing webradio writing mails doing serious stuff.
In X session 2 I login as user2 for the fun part. Here I compile and patch my own wine to play some windows games and use Teamspeak to get the swag out there.
In X session 3 I login as user3 to do the evil secret stuff. Netfilter is knowing my user3 and does not allow him to talk to the network because of his brilliant evil genius.
But I want to hear audio from all users and X sessions no matter which account is the active one. So if I am doing my evil secret stuff, I will hear webradio and the flame war from Teamspeak.
Do you have mpd installed on your system ? If not, I would first consider it. In your case, it will be the easiest way to share a common music library and settings between all your sessions. https://wiki.archlinux.org/index.php/Mpd
If already installed, please share your mpd configuration.