Yeah Bob always puts good arcade hardware on notice in all of his podcasts despite people believing he's biased and gets paid for reviews which he doesn't.
The cbox eliminates the need for an I/O board as a whole. So you can just connect the VGA cable between the Naomi and the cbox VGA port in the back of it
There's a PCB that connects to the jamma looking in port on the back of the cbox , just connect the VGA cable from there to the naomi and you should be able to get RGB off of it