I recently bought an LG 47" LCD HDTV and thought it would be an easy upgrade. When the guys delivered it and installed it they said that the HD converter box and adapter that I got from my cable company wouldn't work with the HDMI cable because I wouldn't get sound. I do get sound if the Input on my TV is set to "TV" but no sound if it is set to "HDMI". I don't see a difference in the picture but I'm assuming that there'd be a difference in the sound. Is there an HDMI cable box that I can get? Is there some sort of audio connection I should get?