Can you be more specific about equipment and what you want to achieve? I'm confused because there is no such thing as a "surround sound." Are you looking at a receiver? A home theatre system with surround-sound speakers?
If it's a home theatre system, it sounds like you're right. The HDMI output from the devices has the picture and sound. The home theatre has one output connection to the TV and switches among the inputs, like your xbox or DVR. So it can read the sound part of the signal and play it to the speakers, and pass the video on to the TV.