Since the only channel you get in 720p is ESPNHD you really should set your 811 to 1080i, because when the 811 is set to 720p it downscales 180i to 720p using it's scaler which is a POS, letting your TV do the scalling will yield much better results?
If you really want CBS and WB there are ways to get the signal directly from the network but it requires a C-band dish, a satellite pc card and a powerful pc, I only bring this up because usually rural folks have c-band dishes lying around