Sling Media's intention is for the Slingbox to be used only by one user to use it at a time. This is actually a feature called SlingSecure described here: (www.slingmedia.com/get/io_1255477160645.html)
SlingSecure means placeshifted content is secured and limited to only one authorized user at a time
* Studio-approved content protection system
* User and device authentication so that only authorized viewers have access to paid content
The Slingbox Pro-HD will allow you to use four seperate video inputs but the SD connections share the audio inputs. So, its best to think of it as one input unless you don't care about the audio for either the S-Video or Composite video source. Like maybe receving a video feed from a security camera. That leaves us with three independant choices: HD (component) connection, SD (S-Video and Composite) connection and ANT IN (coax),
And yes, there is a single digital built-in tuner on the Pro-HD that can only tune in one channel at a time.