I also have interchangeable control panels. I started with a stock ArcadePC mini, removed the HotRodSE, and replaced it with a home-made enclosure with removable panels. I'll submit the project with a URL to my website once I get all the pics up. I used an I-PAC with a DB-25 cable. Since I plan on only having one optical device per panel (too small to add more than one), I just have a USB extension cable inside the enclosure. After this whole project, I have two pointers to give anyone who is just starting:
1) Strip the DB-25 wires about twice as long as you normally would strip a wire and then fold it in half. This thickens it and makes it much easier to crimp the quick-disconnects or to screw into the I-PAC terminals.
2) Buy all your DB-25 cables from the same vendor! I made the mistake of starting with a DB-25 cable which I had laying around. Then I went to the store to buy another one. Turns out, the pin-outs are not standard! So I had to make a matrix of wire colors for each cable.
Here are my panels:
1) Wico 4-way joystick w/red ball, 2 buttons mirrored on either side, player 1 & 2 start buttons across top
2) Oscar spinner, Happ 4-way joystick w/button on top, two buttons on left side, player 1 & 2 start buttons across top
3) Two Happ Competition joysticks, 7 buttons per player, player 1 & 2 start buttons across top
4) Three Wico 8-way joysticks w/blue ball, 3 buttons per player, player 1, 2, & 3 start buttons across top
5) Oscar SWC w/10" Happ steering wheel, Happ 2-speed shifter w/turbo, two buttons, 1 player start button, foot switch (always mounted at base of cab)
6) Happ 3" Trackball, 3 buttons, Player 1 & 2 start button vertical on right side
The enclosure itself has three buttons for coin 1, 2, & 3. I got away with using one I-PAC for a three-player panel because I only have 3 buttons per player. I use the left over buttons for the third player controls. All of the panels are the same shape except for the driving panel, which has a very steep angle in the front and angles down in the back. You'll get a better understanding of all this once I finish my website and submit the project. All the hardware is mounted except for the trackball, which will be done this weekend. I still need to wire the fighting, 3-way, & trackball panel. Everything that's complete works 100%!
Good luck with your cab!
Dan