I have a problem of my own making and I'm willing to admit it. I was so excited to start building my first panel to interface with X-Plane that i made a couple of bad original assumptions that i'm trying now to solve. As a preface, I totally understand that if i would just buy a PC my life would be much easier.
First bad assumption: mobiflight works on mac. It doesn't. I have the Hispapanels MCP faceplate and the matching PCB, and the arduino shield. Hispapanels' arduino shield is designed for mobiflight which uses a painfully different pin assignment scheme than SimVimX. But SimVimX does work with mac. I've temporarily solved this issue by using female-ended breadboard wires so I can cross up Hispapanel's outputs to the arduino so that SimVimX understands what's going on. It looks rat-nesty, but it works, so be kind.
second bad assumption: All multi-digit seven segment displays are the somewhat similar and come in standard sizes. Wrong! The 6 digit displays that fit in the Hispapanels MCP are not a commonly available size. I'm not going to be using the Hispapanels arduino shield set up for the seven segment displays (because it's impossibly confusing to try and figure out what pins on the shield are supposed to go where, considering he's daisy-chained 3 MAX7219 chips). So, I decided the fix would be to wire the displays i have to an arduino manually.
These displays have 14 pins and I've figured out the mapping by messing around on a breadboard. I also have the 3 MAX7129 chips that came on the arduino shield from Hispapanels. But for the luddite, instructions on how to wire this display to a MAX7129 IC are messing with my head!