Another item I wanted to reintroduce to the discussion is the remapping of controls. I have sent a note to a local electrical engineer for input on this issue and am adding the text of that request below.
I could have told you as much as he said.
Here are your programmable arcade interface issues -
First, the available interfaces are hacked PS2 pad, X-arcade encoder, I-PAC, Keywiz, or some combination (parallel wiring to a hacked PS2 pad and an I-PAC, possibly with a select switch, for example). Of these I think the hacked pad is probably the best bet, but more details below:
Playstation2 - Some games let you re-map controls. What would be nice is an interface that allows you to remap the controller - i.e. Button 1 is Square, or Button 1 is X, or Button 1 is Circle, etc. I don't think anyone makes one. The KeyWiz wouldn't work, the I-PAC has a USB option and the PS2 has a USB port, but I think the I-PAC would be identified as a keyboard and not useable by the PS2, the X-Arcade encoder could work and is programmable, but I think the programmability is only for the keyboard mode for PC gaming. The desired level of programmability would require probably a custom encoder chip, new software, and a designer intimately familiar with PS2 signal paths and formats. Even then, you might end up with a programmable PS2 controller that couldn't be used for PC games - - -
MAME - As mentioned, MAME is easily reprogrammed to any keyboard or joystick button, so just about any interface will work. In the case of the hacked PS, you would be connecting through a USB adapter.
PC Games - While many PC games allow assignable inputs, most are looking at keyboard and not joystick/gamepad interfaces, so the PS2/hack to USB adapter probably won't work. The only thing that could work for both PC games and PS2 (other than parallel interfaces) would be the X-Arcade, but it has limited PC programability, I don't think it has PS2 programabilty, and I'm less than impressed with it overall.