Heyo! So I asked a dev and they said:
We don’t do binaural decoding effects, but we use ambisonics with all ambiences in the game. The game is mixed using stereo and 5.1 surround.
We do more than basic panning, we process sounds based on height and player orientation too, and the game is mixed with this in mind (E.g. Filters that give you more focus as a player).
If using Headphones, use stereo headphones option in options, if using a surround system, use the surround options.
Simple enough! We will have a Darktide 101 dev blog on the Sound of Darktide coming out next week ™ which talks more about what it was like to create the soundscape that is Darktide.