DIRECTV SD Receiver D12-100 to Samsung SlimFit TX-R2779H

After much of my own research, I have still not found an adequate solution for my problem. I found one of the rare CRT HDTV's at a thrift store recently. I purchased it thinking it would be the perfect solution to a home setup, only to be dissapointed when I hooked it up. I figured SD DIRECTV would look great on a CRT T.V., but it looks horrible, just like when you feed an SD signal to an LCD HDTV - you can see glittery pixels and horizontal jagged edges. Apparently the T.V. is up converting the sattelite signal, I think? I don't understand enough about the T.V. for one thing. The T.V. has composite, coax, s-video, component and HDMI inputs. The T.V. does something with "1080i/720p/480p/480i". I'm trying to figure out how to get the SD DIRECTV to look at least as good as it does on a non-HD CRT T.V. I'm not sure if the T.V. is capable of displaying in only 480i or if there is a way to turn upscaling off. I have not found an option in the menu for that. Perhaps a certain input will keep the picture at 480i? The DIRECTV SD receiver D12-100 only has composite, coax and s-video out. None of those connections fix the poor picture quality. Just to be clear, I'm not trying get SD service to display in HD. I'm only trying to get the picture quality to be as good as on a non-HD T.V. Would a converter or DIRECTV receiver with component or HDMI out help? Wondering if there's a way to turn off upscaling in the service menu of the T.V. I feel like the T.V. should be able to display in 480i. I read somewhere that although DIRECTV SD is in 480, the compressed MPEG-2 satellite signal doesn't have enough data in it to be upconverted correctly. I don't know if the problem is with the T.V. or the DIRECTV SD receiver/service, or both. Any advice would be greatly appreciated. If I could figure this out, you could watch SD DIRECTV and HD off-air antenna channels, blue-ray, etc. all on one T.V.! Thanks.