As I understand, you want to use a Slingbox PRO-HD and stream the content of your AV source on the living room to a TV connected on your bedroom.
You will need to connect the Slingbox to the router and the cable box on the living room in order to install the Slingbox. Once that's done, you will be able to watch the Slingbox content on the TV using a SlingCatcher or the SlingPlayer for Connected Devices.
You will only need SlingLinks if the router is not near the cable box.
I hope this information answers your concerns.