fireforge, i cannot say what connections you have on the back of your cable box, but check to see that the 'hdmi' to the tv is not coming out of the cable box as a 'dvi' format.
Our newly acquired HD sat box has a dvi out BUT the setup included a dvi to hdmi connector for the output to the tv. That's fine for the video, but dvi does not carry audio. Even the setup guy overlooked this when he was here. Had us puzzled as to why we had video but no sound with the 'hdmi' connection.

"Those who preach the myths of audio are ignorant of truth."