I used a old revision (rev1) of micros neogeo Receiver and put it inside of the A2600 6 swich.
I was modified before with A2600RGB from tim worthington and I used some more switches like select, reset from the Atari and extra button from tim worthingstons 2600RGB PCB
UWRC
Button A = normal FireButton 1 of Atari (Pin 6)
Button B = Firebutton 2 (Pin 9)
Select = Extra Button A2600RGB PCB
Start = Start of Atari 2600
Button C= Select of Atari 2600
Button D = Palette switch A2600RGB PCB
All normal Controllers will work after mod too. Like paddle, racing, joystick.
(diodes, needed to make special functions from A2600RGB working, R=10k as pullup)
RX Led to show it though the power switch hole upperside red led down side gn led