Can you be a bit more specific where you are getting the sound from?
The bravia is a monitor.
The dav dz is a speaker system.
If it's a win7 PC that is the source Type "sound troubleshooter" in the 'search programs and files box' at the bottom of the start menu. Perhaps you have not set the default output device to be HDMI vs. through the MB sound chip.
If the sound source is the DVD player on the dav dz, check the manual, there is a special bravia sync.