The Pandora's Box V3 has support for 6 buttons for each player. I don't have the manual with me, but if I remember right the 5 and 6 buttons wires were the next two after the 1,2,3,4 buttons.
This was a gutted cab, so I did not have any existing wiring except the power supply and the monitor. I bought the Jamma harness along with the Pandora's Box, and it was already wired up to be compatible with the board.
-Max