I confirm strange behavior with 5.1 headset ( logitech g35 ).
It is possible to switch from 5.1 to normal stereo with a hardware switch on the headset.
F.a.e today when i walked i didn't hear my footsteps. I decided to switch stereo and 5.1 back since it seems to fix this issue, but still no footsteps anymore.
So i decided to switch stereo and 5.1 back WHILE WALKING, and it fixed the issue.
The main issue with 5.1 mode is, the sound location seems to be too much directive, and you have to directly face your hear ( left or right ) with the sound source, and if you roll from 10 or 20 degres you don't hear anymore.
Swithcing stereo and 5.1 back seems to work fine.
Hope can help with my bad english. Best regards and congratulation to BIS team by the way.