The documentation for PartyLocalChatControl::SetAudioInput (as well as SetAudioOutput) states that when using Manual selection then the audioDeviceSelectionContext parameter must be the non-null, non-empty identifier of the audio device.
In the absence of any PlayFab functions to enumerate audio devices I'm guessing I would have to use something like IMMDeviceEnumerator::EnumAudioEndpoints to retrieve the devices' Endpoint ID Strings and use one as the audioDeviceSelectionContext parameter.
The problem I see with this is is that the Endpoint ID String is a wide-character string, while audioDeviceSelectionContext is a PartyString (which is not wide-character). Of course I could convert it, but I'd like to have some confirmation first that this is what is expected on the Windows platform.
Also the documentation says to treat the Endpoint ID String as opaque so I have no reason to assume this would work.