If you decode the Combatstick matrix is not need Shift register, and so just adapt CH connector, the one that goes in base PCB for MMjoy2 matrix, and speed the things.

If you opt to Shift Register (no technical advantage in use this instead matrix, but is more "elegant") will be need re-wire each button and HAT corner of CH grip to Shif Register PCB.

How decode the matrix:

Take a multimeter, set in continuity mode.

Put one tip in left pin of CH connect, press a button in grip (a 3rd/4rd hands will help a lot), now start probe the other pins of connector until find one that change multimeter readings. Take note of the pair and wires colors, e.g. 1 black + 5 orange = button 3.

This is the matrix scheme (5x rows/lines x 4 columns) for CH Fighterstick, I guess that for CH Combatstick is used 2 x 7 = 10 buttons + 4 POV HAT

https://s27.postimg.org/j2or5kzsz/CH_FS_matrix.jpg

Finding this combinations is just matter of make a connector, plugged in Arduino compatible with lines x columns you find in the CH connector.

If you don't have a multimeter can make a continuity test prob with one LED, resistor, battery and some wire.

Example:

[Linked Image]

http://www.electroschematics.com/8225/simple-led-tester/

http://www.brighthubengineering.com...ild-yourself-a-simple-continuity-tester/