In my understanding, "Velocity XF" works sounding the note with a value specified by "Velocity XF" (let's say A) instead of the velocity of the note (let's say B), and this function selects either of these using the controller specified by "Vel.XF ON/OFF" on the "Ctrl Map" tab.
However, even if I set the controller specified by "Vel.XF ON/OFF" and change the value to 0 or 127, B is still enabled.
Also, it is unclear that relations to the "Xel.XF" checkbox on the "Perform" tab, but this is able to switch between A and B.
Thanks,