How do I create a startup sound in my home theater?

I want to add the THX startup sound to my home theater. It has a Yamaha main box (well I call it that) Its were I plug everything into. ex. The blueray player, VCR (yeah I know its old). I dint think you can do it without hacking the box or something but it is pretty complected in there and it would not be easy. Is there something I could buy to do that when I turn it on?