It's already a year gone by, but I'll write down my solution.
I'm currently controlling a BOSS Gigcaster (which only "talks" SysEx) from StageTraxx on my iPad.
In StageTraxx I have configured sending CC-Messages.
; CC61 = Guitar FX = U003 THE WALL
[midi@00:00.50: CC61.0@1]
; CC66 = Vocal FX = U002 HALL
[midi@00:01.00: CC66.0@1]
in the background on my iPad the App MidiFlow with the (paid) AddOn for "Controller Remapping" is running. There I configured, the substitution of the CC-Messages to SysEx messages that go to the Gigcaster. So far it works.
