You can use a madcatz fightpad if you’d like. Most of the information on how to wire one up is here on slagcoin?Joystick Controller - PCB and Wiring
I’d recommend it over the EX2 PCB, because it is common ground, unlike the EX2 PCB, which is not. However, if you want to troubleshoot, make sure that you can touch the two quick disconnects together to see if it’ll make X work. If they don’t, then you likely have either a connection problem between the PCB and button, or the PCB may not be working correctly. But, I’d just replace with madcatz fightpad PCB. You can then have a PCB that will let you dual mod, and that’s worth it to me.
Most importantly, this is what to look at when wiring (terminal strip optional)?
However, you should give that whole page a read, and then come back if you have any questions. It’s chock full of great info.