Rather than using that breakout board, you could just use a teensy, it should be cheaper and will documented here. With regards to communication between the MCU and the MAX7219, you may be able to just hook up the equivalent pins (VCC, CLOCK, DIN, GND, and CS) to the teensy and run the code along side the tmk / soarer/ etc iteration that you choose. I have never done this myself, but I know there must be some here with more useful input than myself. I'm more BME than EEE.