Just another thought. What type of HDTV do you have. I think most HDTVs accept 1080i over component cables but I’m not sure they all do especially older ones. If it accepts 720 you should still see an improvement over 480 but if it only accepts 480 then getting any adapter/converter is moot.
Actually could you post all of the models of equipment you are using, HDTV, receiver, and actual video card or motherboard if it’s integrated. This might help us find work-around more easily if there is one.
This is turning out to be quite the challenge.