Should be in <installdir>\UI - that's where it is (on XP64) for both the 32 and 64 bit versions here.
Would you try something please?
Load Max
Customise > Preferences > Viewports (tab) > Configure Driver (button)
Change one of the settings at the top e.g. "Display all Triangle Edges"
OK both Dialogs and close Max
Open Max, go to the same place and see if the setting has "stuck" or if it has reverted to the way it was before.
If the setting has reverted then that particular problem is, categorically, permissions - namely that you, as the user, do not have permission to write in the installation folder. I suspect that as the .xaml file resides within (under) the installation folder that that is also the cause of your menu problem.
Max 2016 (SP1/EXT1)
Win7Pro x64 (SP1). i5-3570K @ 4.4GHz, 8Gb Ram, DX11.
nVidia GTX760 (2GB) (Driver 430.86).