Ok, so I'm an idiot :-(

I'm lucky, empeg have offered to replace my display and rotary knob as a gesture of good faith. However it's going to cost me $100+ in shipping charges and the use of my empeg for a week or two. Don't do what I did - wait for empeg to come out with an 'authorized' solution. They're not going to fix too many (any?) more under warranty.

That'll teach me to read more carefully. Well, you live and learn, otherwise you don't live.