So I finally got the tablet out, and entered the interactive world of this guitar ...
Like I said, the Celtic looking patterns on the Carolan Guitar contain (or disguise) code in their designs, which read by a smartphone or tablet take you to different online places. The first one I tried happened to be the little square-ish one on the side of the body. (It decorates a lid which, when you lift it off gets you access to the pre-amp and battery etc.) I had no idea where this particular symbol would take me, but It made perfect sense for it to activate ... the online user guide.
This user guide has tips from previous players (on how to record this guitar - useful!), but also gives advice on how to change the battery, where to find the volume control etc. The volume control, which had stumped me earlier today, turns out to be a small wheel attached to the inside of the body. Thank you, guitar, for telling me :)
So, once this sorted out, I set up the gear again: guitar in the effects pedal into the amp. Drum machine right next to me. Switch on the camera, and here it goes: