I returned the same exact system because it would take my STB 6 seconds to send the audio to my TV via optical cable. While channel surfing the video will come out and then the audio. I know its not the same exact issue, but the cause is the same. Buying a new cable wont do a thing, its not it. If you want try a digital coaxial cable if both devices support it that is.

Welcome to the world of poorly designed receivers =)