If your cable box only has composite and HDMI connections, you will want to connect the composite cables from your cable box to your Slingbox. You may be able to run the HDMI cable from the cable box to the TV without losing picture through the Slingbox. If you are not able to get video through the Slingbox, or if you get the HDCP error code, you will want to remove the HDMI cable, and run a composite passthrough to the TV. Below are a few articles describing HDCP a little further.
- Slingbox.com - Using an HDMI video source with the Slingbox 500
- Slingbox.com - Why is your HDMI input disabled in Watch on Slingbox.com?
Hope this helps!
Sling Media Support