Just as a follow up, I've been onto Andy at Ultimarc and he's unaware, in this instance, of the need for a jpac too. If anyone could shed any light on what it might add I'd appreciate it. They're quite pricey things so if I can just get away with a VGA666 and a breakout cable, that would be preferable.
Also regarding the breakout cable, Ultimarc sell one, but they also sell a variant called a Arcade Monitor Video Amplifier cable. Does anyone know if this would be a better cable to buy? Perhaps the signal from the pi is weak in some way and might benefit from this cable? Or would the standard one be sufficient?