Hi guys, I've solved this.
Trim back the sheath by around 12 - 15mm. Longer makes it easier to work on, but more difficult to get the connector cover back.
There are three screened wires inside the sheath, red, blue and green. There's also some nylon filler in there which you can just cut back.
Carefully unwrap the three screens from the inners and then twist them all together at the end, about 3 - 4mm. Make sure there are no stray whiskers. This will leave you with the three inners, red, blue, white.
You'll now have 4 ends. Tin them approx 2mm. Careful with the white, the insulation is different and it runs back quickly so take care!
Red goes to tip
Blue goes to R1
Red/Blu/Grn screens go to R2
White goes to sleeve.
Good luck! :)