The multi-zone output on the Marantz is composite only. The only way to use it is to connect your components to the receiver with a composite video cable as well as S-Video or whatever else you are using. I suspect that you have both composite and S-Video going from your DVD player to the Marantz and S-Video going from the Marantz to the TV in your main system. Any problem with the composite video output of the DVD player would therefore not show up on the main system.