Game controller for multiple game systems

I have a problem with my arcade sticks project. I want something like ben heck did with his retro controller for 3 systems

I pretty much have it out of the box i got the ps360+ multiboard wich can do many systems, but sadly no Genesis or NeoGeo.

I tried chaining a Genesis Pad besides the ps360+ and the multiboard is fine with that, but the Genesis pad freaks out and even the Genesis does. It can not boot into a game when the controller is connected and the picture changes brightness. It seems that the 5volts on the genesis pad can go some unexpected routes through the ps360+ board.

I'd appreciate any creative ideas. I do not think i should programm my own multiboard, maybe i am wrong and it's easy but something like a decoupling device was my first idea.

How is this topic related to Arduino?

That’s why i asked for creative solutions. My controller pcb is a programmable atmega microcontroller, too. That is why i come to the arduino forums.