Finally, I decided to build my own buttonbox because even though I own GT3RS wheel, you just never have enough buttons. And I went the same route as other guys did with utilizing an older Genius gamepad with 12 buttons plus 4 directional buttons so I got 16 buttons in total in 4x4 grid. I simplified the PCB as I threw away the PCB part for buttons and replaced analog sticks, 10k Ohms trimmer potenciometers, with 4,7k Ohm resistors and added three jumpers. All buttons except the two on the main PCB are connected in series with 100 Ohm resistors because the resistance of the original buttons. It wasn't hard to figured out schematics as the 2nd pin on CON2A is ground and other pins are for buttons, plus green and red led diode, turbo and mode button. For the box I used fiberglass PCB board (Dangerous particles for lungs when cut!) and soldered it together. Then I cut all the holes and wrapped it up with black decorating film. I made it fairly quickly and the whole cost of this project was just 15€ because I didn't have to buy everything. So pretty cheap. Tested it today with GSC2012 and worked fine. Now to think about what function to assign to it.