Calling all Supratek owners.....

Hi guys I have 2 questions regarding my Chardonnay..I do not have any paperwork on it so I am wondering what the toggle switch on the top in back between the silver transformers is for. When I switch it while playing music I don't really hear any difference. Also has anyone done a dact remote volume control mod, I just want to know if it fits. Thanks to everyone in advance.