I successfully installed a Matrix Infinity on a PS2 V4. PS2 backups work fine, but PSX backups won't load. It tries to load, shows a black screen for a few seconds and then the Red screen saying you should insert a PS\PS2 compatible media shows up. I guess it's one of the wires, but I already checked everything with a multimeter and the wires are as short as possible.
If it is one of the wires, do you know which one it would be?