HOLD THE PHONE BATMAN.
I did a similar project to this and I would love to know more details on what you did. I took the PCB of the controller, unsoldered the triggers and joysticks and then I connected digital potentiometers to replace them. It worked flawlessly with controlled input.
That being said, my buttons were nightmares. I used an exacto knife to scrape the trace and solder to that tiny tiny piece with enameled wire. It was terrible and unstable. How are you handling your connection to the buttons? I think this project is great and glad someone else has a similar interest!