From your iPhone/iPad, select the "Stream to audio|acacia" option in the AirPlay device menu. This feature should work for any app that supports AirPlay audio output (e.g. Spotify, Pandora, TuneIn, etc.).
Navigate into System Preferences > Sound > Output, and then select the "Stream to audio|acacia" AirPlay device.
Select the "Stream to audio|acacia" AirPlay device.
The AirPlay streams are accessed via the AirPlay source from the left-hand drawer of the controller app. audio|acacia has the unique ability to accept multiple AirPlay streams simultaneously. There is no known limit to the number of incoming streams. Each active incoming stream will appear within the source, labeled by the device name. Pressing the play button will begin playback of that stream to the selected listening session. If metadata is sent by the AirPlay-enabled app, it will appear within the controller interface.
Note: In order for the "Stream to audio|acacia" option to appear, at least one audio|acacia server must be running on the network. Also, currently audio will not be in sync with video, though this is something we can add via a software update (vote for it here). Lastly, playback (e.g. Play/Pause & Next/Previous) of the AirPlay streams cannot be controlled within audio|acacia, but this can also be added via a software update (vote for it here).