Ideally, you'd have a receiver that has multiple HDMI inputs. Your DVD player and TW Cable box would connect via HDMI to the receiver. Audio out go from the receiver to your surround sound speakers while video would display on your TV.
DVD Player --> Receiver HDMI Input 1 --> Audio Cables --> Surround Sound Speakers
DVD Player --> Receiver HDMI Input 1 --> HDMI Output 1 --> HDTV HDMI Input 1
TW Cable Box --> Receiver HDMI Input 2 --> Audio Cables --> Surround Sound Speakers
TW Cable Box --> Recevier HDMI Input 2 --> HDMI Output 1 --> HDTV HDMI Input 1
-Wolf sends