Humble apologies to Martin and Tido. I ask for advice and don't take it. There is a reason, age, if I patch things and it works, sure as hell in a few weeks when I want to make a change I'll have forgotten or lost the links to the changes.
I have wired in the PCF8574, it works with no changes to the system. Crazy, when all those pins are sticking out of the Rock64, defeatist maybe but it is working, I understand what is going on and I can tidy things up now.
If Armbian ever fixes the GPIO I would pull out the 8574 and go direct. It's tidier.