You are going to need some sort of interface to go between the controller and your Pie. You will need to connect your buttons either to a device like a “teensy” controller that can map the button presses as a HID (human interface device) or use them so they can connect to the GPIO pins on the pie. In this case it will be a long drawn out process. I think that if you are looking to keep the integrity of the controller together, then using the USB adapter is the way to go.