This is only partly a Nixos problem but pipewire doesnt seem to have forums themselves.
Basically, I have an audio device behind a displayport connection to a display that I want to use.
Using aplay -l or aplay -L I can see that the system recognizes it:
$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: NVidia [HDA NVidia], device 3: HDMI 0 [G27Q]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 7: HDMI 1 [S32B80P]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 8: HDMI 2 [HDMI 2]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 9: HDMI 3 [HDMI 3]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: Generic [HD-Audio Generic], device 0: ALC1220 Analog [ALC1220 Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: Generic [HD-Audio Generic], device 1: ALC1220 Digital [ALC1220 Digital]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 3: MICROPHONE [USB MICROPHONE], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
The device in question is device 7: HDMI 1 [S32B80P].
I can listen to output via aplay without problems using aplay -D hdmi:CARD=NVidia,DEV=1 ./Downloads/Free_Test_Data_1MB_WAV.wav .
However I still cant find out how I register it in pipewire so I can actually use it as a sink. 