@TVsIan Glad to hear that it is working for you now!
@ortsac The driver polls the terminal pins on the player 2 side of the board and that's really all: If the SNES controllers are not connected to those specific pins, no data can be read out.
I will prepare a schematic for that part of the ControlBlock soon. Basically, the driver communicates with the two GPIO expander components on the ControlBlock via SPI. Nothing more fancy happens there.