Thanks for helping me out earlier via email Burkhardđ
Incase anyone else stumbles across this, I wired the kones in the exact same configuration as the previous 16ohm G12s that came with the marshall cab.
After testing each jack with a multimeter I can confirm the 4ohm jack now runs at 1ohm, and the 16ohm jack now runs at 4 ohms, as we speculated in our earlier conversation.
I tried to wire it as per the kemper diagram, but you have to have wires going to both the jacks, otherwise I guess it doesn't complete the circuit or something. Wasn't getting a reading when only one jack was connected.
So I've taped up the 4ohm jack, and all running smoothly now through the 16 (which is now 4đ)