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 =)
I am having dropouts, I have an AppleTV and a DirecTV box connected via optical cables. it happens all the time on both connections and its driving my wife nuts. Is any one else having these issues? I may try buying new optical cables but I don't think that is the issue because I did not have this problem in the past with my old receiver.