Here’s an explanation from Naim support about the RCA to DIN Superlumina design (quote copied to save clicking through!)
In the case of a naim system the “preamp chassis earth” is connected to the “signal earth” inside the preamp. Since our preamps have external power supplies the signal ground is used as the preamp chassis screen. Note that in the following description “ground” or “system ground” is the negative or 0V reference of the system and “mains earth” is the earth connection supplied by the mains lead and plug.
In this customer’s case (of an RCA to DIN lead) the RCA connectors will have the signal and ground connections using the individual conductors soldered together. The white sleeved cables are the ground and the red or black sleeved cables are the signal. In addition (since the RCA’s are the source end) the screen will also be connected to the ground via a padding resistor. The resistor is there to control the characteristic of the screen “seen” by the ground.