Well, I'm not sure...I have different choices :P
If you select that input, I fear that you'll get a noisy signal, but you can try..
What did you get when you select "What U hear"?
I suggest you to try them all..
To know which filter is used by BS.Player: with a movie loaded right-click on BS.Player window -> Options -> Filters -> Advanced
The error message when devices are opened multiple times will be fixed in a future release, not this week