Uncle Tom, who is an arcade collector just like me, only 10 times more hard-core
gives the following homebrew tip. It's easy to make, inexpensive, and if you connect it via USB gives the quickest response. It also works with every single emulator out there.
1. Get an old keyboard, the one with a real printed circuit board and not plastic overlays inside.
2. Connect the joystick's ground to the keyboard ground and the 4 directions and fire to the keyboard switches of your choice (preferably one that matches a WinUAE config). (Buy a 9-pin female joystick connector from an electronics dealer.)
We would do it to be able to use the superior arcade joysticks with blade switches that we love, and play MAME with no joystick lag. It's meant for building a PC & screen into an arcade cabinet and run MAME with arcade feeling, if you do it you might wanna do a little box for the keyboard PCB