Support passthrough via pulseaudio
Should be backward compatible and not enable on systems with older pulseaudio.
If your pavucontrol mixer doesn't allow you to set supported output types, you may need to use something like:
pactl set-sink-formats 0 "pcm; ac3-iec61937; dts-iec61937"
To signal that your audio sink support ac3.
It should after that show up as available devices in the passthrough audio selection box.