When updating from a 7202 to the XG-8... things were very cryptic and believe the manual expected a more current understanding. I muddled through it but and at times struggled and asked questions as you are doing.
Wish I could be of more help. One thing I did wonder from your question, is if you should be looking in the Xbus menu instead of the wing setup for assignment of servos for xbus use. In that regard, I recall that the release firmware for my XG-8 did not include the Xbus menu item but the vs .015 that I later loaded included it. So...if you do not have an Xbus menu item in the TX... a firmware upgrade will probably be needed.
If doing an upgrade... be certain to follow directions to the letter because you don't want to end up with a deaf brick.
Best of luck.