Midi is just a form of serial interface, specifically designed for use with musical keyboards - although much other midi equipment has since appeared. The chip that has 'Midi-decoder' stuck on the top is probably a PIC, or other micro-controller. Because it was designed with music in mind, it specifies an opto-coupled input, in order to prevent earth loops and hum.
I can see it would apply well to your application, because it already does much of what you want - allowing you to have just a couple of wires from your firing position, and individual control over many channels.