We're going to have proper preferences in the future. But if you want to do some manual adjustments in the meantime, check out these files...
I recommend you know how to use a text editor like Notepad++. Basically, just change a few numbers, save (in admin mode if necessary), then restart Sansar.
DISCLAIMER: FEEL FREE TO EXPERIMENT, BUT THIS IS NOT OFFICIALLY SUPPORTED. IF YOU MESS SOMETHING UP, REINSTALL SANSAR.
See the in-file comments. You can change overall UI sound levels in here, as well as levels of specific UI events and background music.
This is another way of changing overall UI sound, as well as footsteps (in 1st- and 3rd-person view — note that there are NO footstep sounds in 1st-person VR).