ARC Ref3 Bal-SE button..what for?


I was wondering what the BAL/SE button on the ARC Ref is for? I have my cdp connected to the balanced inputs but when I push the BAL/SE button on the Ref 3, I still hear music. Can someone please explain what this button is supposed to do?
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Maybe that's why I thought the Ref 3 sounded thin in my system.... I had a dealer loan without a manual...

Thanks for the corrections!
Chris
Mitch - after looking at your system - I'm afraid my photo's would be quite boring in comparison!! :)