I understand that you want to know how to take advantage of the Slingbox PRO-HD internal tuner.
The internal tuner of the Slingbox PRO-HD allows you to "split" the TV signal. This specific setup will allow to share the TV signal, although the users will share a different TV signal.
The basic way to connect the Slingbox is to place a splitter on the cable that comes from the wall. From the splitter, you will send two lines: one to your Slingbox and the second one goes to the cable box. This way, the Slingbox will allow you to split the TV signal.
Finally, you can also connect a different type of cable (S-Video, Composite and Component) from the cable box output to the Slingbox inputs in order to take advantage of the other inputs on the back panel of your Slingbox PRO-HD. Just keep in mind that besides these connections, the Slingbox will allow only one connection at the time.
Hope this helps!