Edward, thank you for your thorough reply.
They had set the old desk up so that a handful of important fixtures had their channels patched onto the Presets in blocks of 6 (intensity, red, blue, green, white, not used). I had assumed at first that the heads were set to first address 1, 7, 13 etc. to achieve this but when I dug into the config I could see that the higher DMX numbers in the 100s were patched accordingly. Whilst it means the operator could colour mix on faders it would presumably conflict with LTP on the desk.
Regarding intensity, can each of the 48 dimmers be patched to multiple DMX addresses in parallel or is it one DMX per dimmer/fader? That will get round multiple heads with the same start address with them running out of blocks of 6 faders.
Whilst you are on, can I output DMX universe 1 to both desk outlets 1 & 2 simultaneously? That will sort out a short term wiring config to match the current arrangement.
I have looked at the manual and tinkered with GhostZerOS but I haven't quite got my head round the subtleties of setup yet.