you need to buy external RDC. KRC supports up to 4 RDCs. one is already in the robot.
out of those 4, up to two can be daisy chained (cascaded). this allows you to add another RDC without modifying KRC4 controller and adding second RDC interface. optionally you could modify cabinet and add the second interface (plugs into CCU, X33 and X34 are for RDCs).
so data cable would go from KRC4 X21 to new RDC (mounted at or near KL). then from new RDC (through cable track) another cable to the robot (old RDC).
btw, you want to connect E1 (KL) also to this new RDC.... unless you don't mind running more cables through cable track and those are subject to wear and tear.
next you will need to adapt topology.
first you need to be able to see the actual RDC data connections.
so right click on drives configuration page and under layout select Show fieldbus members
this will allow you to see planned connections and make sure they are correct. here is default (parallel)
to modify connections, edit KCB topology, save it and thecn check this again to verify that change took place
next you will need to assign correct FSoE ID to that RDC using WoV (check WoV help for instructions).
yes... cascadable has two connections so it can be in the middle between robot and KRC. i think it may already have FSoE assigned as default...
that is the simplest and most common way to upgrade. it means no hardware changes on the controller and there is no leftovers, you just need to by things that are needed. connect resolvers of all external axes to new RDC.
when editing project EMD can be on either of the RDC, don't forget to link robot and KL kinematics and setup transform for your robot.
but ... who knows, i may be purposely trying to deceive from time to time. what if you are the lucky winner... 
I think it is the same on Kuka 3 axis positioner. you can get those in your KP3 positioner.
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yup and if i recall, KP3 should already have the RDC.
