Can someone give me the quick explanation of how a camera gets on a TPS-2000L without using the videoencoder?

Got a potential client with a CP2E, PAD8A, Amps, Escient E120, and DishNetwork receivers.

Now, on the 2 TPS-2000L's he has in the home, he is currently getting a camera feed to the panel and a dishnet feed to the panel. How are these 2 different sources getting routed to the panel? I thought it only had 1 video input? Obviously an older system, but they want to add some more cameras. Wanting to see if this is possible and how I can go about it the easiest way (adding 2-3 more cameras to the touchpanel). Money not really a huge option.

Thanks for any help you guys can provide. I much prefer this forum to the yahoo group.