Thanks Elektrofon and Giedrious. I had to manually add these two config.txt lines above on my original full-fat build (with monitor) to work. The automated install script ran but didn’t add these lines (tested twice).
I’ve had a look but cannot find config.txt on the Pianoberry fileset. Are these unzipped on boot? If so, not sure how I find config.txt and edit without a monitor. This is where two days of Rasberry Pi and linux is letting me down - my apologies.