I constantly run into set ups where I can't get sync two things together because I can't point that far. This is a good example of it.
(1) If you make a custom control surface and add a multi button
(2) then go to your layer one opacity, and create three marks
(3) then try and sync those marks to your buttons...how do you do it?
? if you go to the layer opacity and hit the drop down all you can see is the "multi button", not the individual buttons.