Cheers Alex, any improvement can only be from your generous and patient mentoring.
I don't know about "worked out", it took much clicking and gnashing
The short version:
- Load the files from each setup as a separate session
- uncheck "same camera and optics" in the register tab
- select "integrate per channel" and "integrate all & per session" at the top in the integrate tab
- integrate.
I probably forgot to do something important but that's how I bumbled through.