IIRC the Naomi has the Maple bus available to connect a pad there. You may need an adapter. Something that is not clear is how many games will accept input from both JVS and Maple.
Probably the easiest for you will be something like this:
An economical way to build a naomi arcade cabinets
$75,free shipping
The new version adds incremental purification function
DC JAMMA Converter
It is used to play DC games on the arcade frame. It supports low-resolution JAMMA and high-resolution VGA output modes. It can be switched by key. It is suitable for ordinary low-resolution frame (AC) or tri-band frame (NNC). The sound can be selected in stereo The output is connected to the power amplifier, with its own memory card function.
How to use: The DC signal output connector of the converter is inserted into the video output interface of...