IIRC, TTrackButton only specifies which button(s) can be used to "click" a menu item, not which can be used to popup the menu itself. This last, again IIRC, is widgetset-dependent and can't be easily changed: one has to use some workaround---like, say, intercepting mouse operations.
As for AutoPopup, I've never used it but according to the documentation it's used to popup the menu whenever the mouse hovers over the corresponding object, but this is probably wodgetset-dependent too.