I tried usind three different digital optical cables to make sure that is not the problem. Also movies that are lower file size like 800 mb play fine through usb through stereo. It seems the high res files are having the sound interuptions every few minutes. I have tried two different HT-C550 units and same problem exists. Hope this extra info helps.
Thanks for reading.
Purchased 46" 120 mhz model 610 TV. When I play a movie using the usb port the picture and sound work without problem. When I play same movie using HT-C550 home theatre system the sound cuts out every few minutes for a duration of about 1.5 seconds then starts working again. The sound appears to be in sync when it is playing. The only cables being used is a digital optical cable between the TV and home theatre as I am trying to track down where the problem is coming from. Any answers?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic