I have a sony EX720 connect with sony DAV DZ840 home theater system using HDMI cable. Now when I play movie from portable drive connected in the USB of DZ840 system, the sound system works fine. Now when I watch normal cable channel in the EX720 tv and set the DZ840 function to TV there is no sound coming from the home theater system. But If I turnoff the home theater then sounds coming from the TV. How can I get the sound from DZ840 system while watching general cable channels in the TV ?