Hey Nate!
Have you gotten your music to start playing when the first wave begins?
If your music layers are synchronous, you would want them all to start at the same time but with the volume set to zero on the additional layers. Then when a new wave starts, you change the volume of the corresponding music layer so that it’s audible.
I can’t tell for certain if that’s what you’re trying to accomplish, but if you’re just trying to get something to happen (play music) when something else happens (begin wave), you can create a custom event or an event dispatcher.
Let me know if you want more help with either of these, or if I’ve entirely missed what it is you’re asking.