It’s in the youtube video, I’ve added a timestamp for easy viewing: https://youtu.be/pHe8ZuOP6Xs?t=86

We now know 6 axis IMU is for the “spatial audio” which allows for “dynamic head tracking”, where the audio won’t move with your head! It’s a pity that you can only apply the firmware update with an Apple Device. If you don’t, you’ll need to go to an Apple Store to apply it