It would be nice if someone could make a guide showing which wires to connect to get an Ave Pad 6 working with a PC-FX controller plug. Just to have a decent d-pad for the games which need it.
I
think that you're going to actually need a circuit board for that ... the
impression that I get from the PC-FX docs is that the joypad port is clocked-serial and not nibble-based like the PC Engine.
I'd love to be wrong on that, but I don't
think that there are enough pins on it to do the full 2-way communication that it supports if it were using anything other than serial shift-registers.
A real hardware-guy could probably figure it out pretty quickly.