So I couldn’t get 4-Up working properly as the link kit just mirrors the controls over both cabs. However after discussing it with Invizm, we came up with a way to make it work. You need two JVS Expanders. Only one of them needs a DE-10 and the other connects to the first via USB. As long as they are both on the same firmware, everything will work as it should. The cabs are now both VS cabs as well as 4-Up. This is controlled by whatever Start button you press after credit input. You can sit anywhere you please for VS, which is an unexpected bonus. The only issue is that some games cannot be played without messing about as they require four coin mechs. Free Play does help a little, but not for everything.
Fortunately I had bought a second JVS Expander in his moving sale as an impulse buy because it was cheap and I was able to get it all up and running following a bit of tinkering.
Now I just need to get my new PCB boards back from the cutter and then rejig the cable system so that it is nice and neat to house a main PCB on top and a JVS Expander underneath.
I thought I was finished before, but it seems not!