There are two different A/V connectors standard that the minigun uses. Your board will have either an eight or nine pin mini DIN A/V connector. You can buy a premade cable for either one.
The CPS1 multi is available and plays all CPS1.5 games, including Cadillacs and Dinosaurs. Converting CPS1.5 games to CPS2 doesn't make much sense any more.
I don't think this would make a difference to anybody who cares about the existing original vs FPGA qsound implementations. It certainly wouldn't get me to change up my CPS1 multi setup.