Zenith HDSAT 520 Directv receiver question

I have had the Zenith HDSAT 520 D* receiver for quite some time hooked up to my Samsung HLN617W DLP. I am beginning to wonder if it would be beneficial to watch standard definition programming via the S-video output of the box at 480i rather than the DVI output at 720p (which looks really horrible at present). Maybe the up-conversion takes away a little clarity of the SD broadcast. The only reason I am asking is because I haven't had the time to calibrate any S-video inputs of the set and the color, tint, etc are all off and I cannot tell by looking so maybe if someone has first hand experience it will save me some valuable time. Any replies would be greatly appreciated.