The digital audio output will likely be dependent on the cable receiver - whether a set top box provided by the cable company or a cablecard tuner built into a TV. Some of the Scientific Atlanta HD boxes as well as all of the Pace Micro boxes include analog-to-digital converters that produce a digital signal from those analog channels, allowing the box's digital audio output to always work. I'm not sure about Motorola and Pioneer boxes, or about the current batch of cablecard tuners in TV's.