ok, yes step missing... oops.
In controller/surface properties, (on menu bar in Plat, dont remember about x3 though), choose the main unit and click the little properties button.. on the bottom right of the new window there is a layout button.
click that, then use the first pot/knob to scroll through channel choices on both the unit and ext.
When set, press that button again.
It should save the setup and you should have 16 channels in the order you chose.
I always had issues until Platinum, now it works great.
https://www.cakewalk.com/...xternalDevices.07.html25