The Tunecast II will turn off when it's not transmitting sound. It should turn on automatically when you start your light show, if you start it loud enough.
In my audio startup, I generated a five second sine wave that goes off to turn it on. Regardless, you will have to keep music going through it to keep it on.
Now, if you run down to Radio Shack (this is what I did), they'll find the AC adapter plug to go into it and attach it to a universal transformer. Trust me, you don't want batteries, and if you havn't done it yet, do the antenna mod.