The itunes is an interesting idea.
But what you're talking about in that case I believe is a sort of "remote control", where you have Itunes running on your cab, and you use your phone to remotely control what the cab plays.
No idea whether Itunes will do that, but I do know that JRiver media center has functionality like that. I have it running on my server, which is hooked up to an amp driving my patio speakers.
I can use my phone browser to navigate to server:8080 and I get a web interface that can control the copy of media center running on the server.
I'll be doing the same thing with my jukebox build.