you could have a timer trigger that will have event that gose off every ( lenth of music) and then play sound and reset the timer to ( lenth of music). example.
Events
Map initialization
Time - Timer_music expires
Actions
Wait 0.01 seconds
Sound - Stop music After fading
Sound - Play Music
Countdown Timer - Start Timer_music as a One-shot timer that will expire in 30.00 seconds
Music
Events
Time - Elapsed game time is 0.10 seconds
Conditions
Actions
Sound - Stop music Immediately
Sound - Play Song <gen>
Sound - Set the music list to Song <gen>, starting with a random song
Or better yet just check the box "loop" in the sound editor while editing the properties of the sound. Then just play it once and it'll keep on going until its been stopped via triggers.