I recently purchased the DAV-DZ810 system. The surround sound is working and I get sound on all the speakers when I play DVD. But when I switch it to TV to watch cable I do not get sound from all the speakers, only from the front speakers eventhough I selected the option to have all speakers on.

When you play a DVD, the sound source on DVD would be 5.1 encoded. Means that all the speakers (5 speakers and sub-woofer) would get the sound. But when you receive the sound from TV it would be a Mono sound (Unless you have satellite dish receiver which would be Stereo) So you'll only get sound in front Center speaker. If the sound source of TV signal is Stereo then you'll get sound in Front Right and Front Left speakers. Some receivers have capability of 5.1 channel also. Basically it is the source of sound which your DVD players receives and encodes. Hope this helps.

Please check the connections TV - o/p and DZ810 - I/P ports..!!