Personally I would use a different device for "confidence checking". If you are streaming the main mix it is independent of any speaker feeds but I wouldn't mess around with the PC sound settings while streaming.
A feature I would like on PlayIt Live is a "monitor selection" facility so that the selected headphone output could be switched between streaming output, each of the players and the normal cue/prehear output, in much the same way as PFL on a mixer works.
Is there a sound mute button? So i can check (sometimes) my own streaming to listen over the speakers for sound checking?