The zone outputs are only available when an analogue input is being used. If you currently have only a digital cable connected from a source, a separate stereo analogue cable should be connected to the same input to allow the source to be heard in the remote zones.
Digital audio signals and analogue audio signals are kept separate from each other. The multizone circuitry in Rotel surround receivers and preamp/processor is analogue. If you have digital connections from your CD player or DVD player to your home theatre receiver or preamp/processor, you must also use analogue connections (RCA connecting cables) from your source components to the CD or DVD player input on the receiver or preamp/processor.