I have a Sony Bravia and Sony Home Theater System with DVD. When I play a DVD the sound comes out of all 5 speakers. When I play the TV there is no sound from the speakers..just the TV Speaker. Do I need to connect audio cables from TV to home theater system? I was told I don't need audio cables because the HDMI Cable takes care of both the audio and video. The HDMI cable is connected to the home theater system and the hi def cable box. Any suggestions? Thanks.