Pimax support said that the right jack is reserved for MAS and won't work with anything else. It didn't work with normal headphones but did work with 3-d party Oculus Quest headphones
Reality checking the hype train on the Pimax 8K PC VR system : r/oculus
The Pimax 8k X is hands down the most immersive & beautiful VR headset I've used so far. : r/VRinAZ