if you want to use xplane 11 to program the buttons, then you must un-assign the buttons using the brunner buttons tab. Once they are un-assigned xplane will “see” the buttons and you will be able to assign them. I use a combo of brunner software and xplane software. So for example, button number 1 is assigned using xplane as contact atc. In the brunner software I have button 1 un assigned. Button 2 is trim down in brunner software. Xplane does not recognize button 2. However, the command of trim down does work, because brunner is telling xplane about button 2.
Hope this helps.