I don't use the Columbus yet, but I use the Engl Z12 which I believe is similar.
I am not sure what side you are having the trouble on, but on the G Major 2 side you have to go into MIDI, set midi chan to omni, push the down arrow and set midi prgch "on", push the down arrow twice (skip the bulk dump part) and select prg bank "custom" and then click the right wheel. Then, select the PC (prg chg1,2,3,4,5,etc; this will refer to the button on the Columbus) and push the down arrow to select "map to" and which preset you want like factory 36 or user 2 etc...
Let me know if that's what you were having trouble with and if that made sense haha...