I'm not sure if I'm reading the diagram on the website properly...  This is what it says:
The connections for the 10-pin header are as below:
Wire Input Mode Output Mode 
Black COM Connect to COM terminals on all buttons GND. Connect to I-PAC if required 
Brown Button 1 NO not used 
Blue Button 2 NO Down Digital. Connect to I-PAC if required 
Orange Button 3 NO Right Digital. Connect to I-PAC if required 
Yellow Button 4 NO Left Digital. Connect to I-PAC if required 
Green Button 5 NO Up Digital. Connect to I-PAC if required 
Red Button 6 NO 5 Volt supply. Not required if USB is connected 
Grey Button 7 NO Raw analog. Not used at present 
Violet Button 8 NO Raw analog. Not used at present 
The optional wiring harness has cut wire ends which you can crimp suitable connectors onto, for your pushbuttons. There is one ground wire which you will need to daisy-chain to all COM connections on the switches so you may need additional black wire to do this.
The supplied wires are 18 inches (450mm) long.
The black goes to ground on one of the buttons and I can daisy chain the rest of the grounds together ending on the last button.  Is there any particular default order that I should wire the rest of the buttons to minimize configuring everything?  I've got three action buttons, ESC (to exit to frontend), P (for pause), 1 (for P1 start), 2 (for P2 start) and 5 (for the coin door - no button on the CP).  What color wires go where or does it even matter?