If you go into the 6412's menu, (power off on dct, then menu on your remote), there are lot's of options to change. I think it's the 2nd or 3rd option down, I think it's called "4:3 overide", you can choose something like "stretch, 480p", etc...try using "480p", at least on my 46" Samsung DLP it stretches the 4:3 anolog and digitals to fit my screen and I think it also upconverts them to 480p, making these particular channels look 10x better. Using the "stretch" option, it does pull the image to fit my screen, but the channels don't look any better, same as the internal TV stretch modes don't make the channels look any better, just makes them fit the screen. So try "480p", and see how that works for you. (if you have a TV that supports that mode of course).
It does nothing of course for HDTV, the 4:3 HDTV channels are still 4:3, and whatever resolution they are broadcasting in remains the same 1080i, etc...which is how it should be.