Connect your cablebox to your slingbox using component video cables to the component video input(s) on the back of the slingbox. Then connect the component video outputs of the slingbox to the tv's component video inputs.
By doing the above, you will acomplish 2 things:
1. you'll be able to stream your cable box in full HD resolution (1080i) within network, and also remotely (as long as your ISP has the required upload bandwidth to support the stream).
2. you'll bypass the HDMI copy protection scheme implimented by the cablebox.....
Your not loosing anything by doing this since your cablebox is only capable of outputing 1080i....
Wala, sistuation resolved