Are you sure that the cables are not faulty? Have you tried swapping them out/around and/or trying both powerlink sockets?
If you have a multimeter, check the continuity of the PL cables – pin 6 is data and pin 7 is data ground. Make sure that pin 6 isn’t shorted to one of the other connections.
It’s also worth disconnecting anything else from the BeoSound (Masterlink and Aux socket) to rule those out as part of the problem.
