Thought you all my be interested in this. One of the regulars at KLOV forums has produced a JAMMA pass-through adapter that provides a separate RGB output.https://forums.arcade-museum.com/showthread.php?t=392389
A Mike's Arcade Nintendo-to-JAMMA adapter on the unused edge connector -> JAMMA pass-through -> taking the video output to a Gonbes 8200 or JROK encoder can get you direct feed output from the edge connector pretty easily. It also has a break-out header for +5v, which would provide power to either of those solutions. You could easily solder audio output to the audio lines at the unused side of the pass-through adapter, to get audio for your direct feed as well.
A bit simpler than my current direct feed solution. Considering getting one of these pass-through adapters for one of my JAMMA cabs.