I can't see enough of what's going on here. Is "Music" a global variable?
I think what you need to do is create global variables to define the exact music files you want play and use the "System object to set the URL of a music file. For example:
Create a Global Variable
Global Text = "URL_1"
System> On Start of Layout > System> Set URL_1 to
It's a simple example but, should get you in the right direction.
Hope this helps