Setting audio output device in FMOD and OpenXR

Using Unity/OpenXR and FMOD (for PCVR). I have an issue setting the correct output device in FMOD.

FMOD plays in the default Windows device, and Unity sounds plays in the headset, so Unity knows the device… but I know no way of getting it from Unity/OpenXR. And it is not enough to just guess the name of the device (possibly "Oculus Vitual Audio Device") because the name is not included in the device info from FMOD, and since I build for Steam there could be other devices for other headsets… So I really want the device GUID used for This headset, from Unity/OpenXR.

How can it be done?