The Pi2Jamma comes with a GPIO female connector and will be plugged directly on the Raspberry Pi.
The Pi2Jamma has a Jamma Interface. The Jamma harness will plugged on the Jamma connector without any modification on the cab. Parts side is the top Side.
For Audio the stock audio cable will be plugged to the audio connector of the Pi2Jamma and Raspberry Pi.
Volume control is on the black potentiometer on the Pi2Jamma. Adjust it to your needs.
Button 4, 5 for both Player is on Jamma Connector Pin 25 and 26 and bottom side. Bottom 6 for both players is available on the screw terminal. The screw terminals has also one GND.
Raspberry Pi is powered via Jamma. Again, there's no need for extra power, just Jamma interface. Raspberry Pi has over voltage protection. Its safe to use up to 5,2V
Installation steps
You should see menu booting up. Congratulations you can now start copying your roms to the USB Stick.