s-video question - DirecTV DVR

For s-video question, relating to DirecTV DVRs and receivers. I am using Monster Ultra THX 1000 S-Video cable to connect my DVR to my Samsung Plasma TV. The picture is not quite as sharp and detailed as say my DVD which uses Component Video cables. Would my picture quality improve if I used some of the even more expensive Monster S-Video cable or is there a limit on what you can expect with S-Video. The S-Video cable I am using is pretty near the top of the Monster Cable line. Also I noticed that some channels like National Geographic just seem to always look better than others. Is this just the way Directv recieves the signals and some channels will never look that great.