Tonight's build allows playing the audio that's going to the default Windows sound card through the JRiver engine. It does this using WASAPI Loopback.
This is a poor man's virtual sound card. It can't do latency compensation, so if you use processing that adds latency, lip-sync will not be perfect.
To use this feature, you need to set the default Windows playback device to something other than the device Media Center is using. Then, start playback in Media Center using:
File > Open URL... > live://loopback Using a small buffer size in Options > Audio > Output mode settings... is recommended.
Sounds that go to the default Windows device will also go through Media Center.
As an example of a real-world use for this, I have a Desk and Theater zone at home. The Desk zone is where sounds from web browser, Netflix, and games go. When playing in the theater, I need those sounds redirected to my Theater zone where Media Center does bi-amping, etc.
I can now start the Theater zone playing live://loopback and then play a game or Netflix on the projector and get nice sound. Previously, I could switch the default Windows audio device but since Windows doesn't know how to handle the bi-amping of my subwoofer, all the sounds went to the wrong places.
Please keep in mind that this is an experimental project. There's no guarantee it will remain or be developed farther for v17.