Hello mate
You can only have one playback device at any one time. Each of your monitors will be designated a playback device.
So what that means is this, only one sound stream at any one time. Either to your speakers, the TV for your GF to watch a movie or to the monitor.
There is no way you can stream a movie to the Telly and game at the same time, both sound streams will be active. However if you want to game with the sound muted I guess you could.
Hope that makes sense to you.
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