Why not just go from cable box directly to the TV and bypass the HT receiver altogether. This elimnates any conversion and a 2nd video cable as well. Surely the TV has multiple inputs so use one directly from the cable box and if you have many other video sources, run those through the HT receiver and have that drive another TV input. I'm a big fan of not using the video switching of a receiver or preamp/processor to keep the video signals isolated from the audio signals going through here. This is the best way to take advantage of the HT sound system. And if you have a programmable remote, you can configure it to choose the source on the receiver and the corresponding input on the tv at the same time.
John
John