And here I am getting rocked by the second stage boss! Nice one @roker.
There's a translation patch here btw: https://www.romhacking.net/translations/1075/
IMO the stick sucks for fighting games, it’s ok for puzzlers and NTM but otherwise you need a proper arcade stick. For example even something like a double tap to dash is more difficult than it should be on these. I can’t comment on the original CD pads as I never had one.
It might not need -5V but rather it’s possible the speaker + and speaker - lines are swapped. That would cause it to not have sound on a supergun but have sound on a cab. Some boots are like this.