I received this reply from Naim in connection with the RCA to DIN Superlumina source IC. The same principles apply.
The website has this description of the superlumina interconnect cable:
“The fundamental cable design consists of several individually-insulated multi-strand silver-plated copper conductors of varying diameters enclosed in a tin-plated copper shield. This is all enclosed in a soft outer jacket which facilitates easy installation whilst minimising microphonic interference. Each signal, return, ground and shield conductor is individually manufactured for its specific function.”
As is obvious from inspection of the cable the screen (referred to as a shield above) is separate for each channel.
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.
The overall screen in a cable is there to "protect the signal”. It has to have a connection to the system ground at some point, or it won’t work as needed. Note that system ground is not the same as mains earth, ideally they should be connected together at one point (usually at the most often used source), but in most cases a system will work without problems “floating” from (as in not connected to) mains earth. We would always recommend that a system has its system ground connected to mains earth for best sound quality.
There is always an earth loop when using RCA connectors in a stereo system; as long as the two channel’s cables are kept close together it will not cause a problem. If they are split and are routed far away from each other there may be some mains hum picked up. In the case of most audio cables the two channel’s cables will be joined together by their overall sleeve and so will be kept close together. This is one (of many) reasons we prefer to use din connectors for signals between parts of the system.