Hitachi 57S500 has terrible DVD playback

I've noticed that this is true, just as cnet.com says. But they also say (as do many other sources) that this is the top Rear-Projection for the money. I watch in the regular scan since progressive scan makes everything worse. I'm thinking of getting a Samsung 731 1080i upconverter but am skeptical that it will truely upconvert anything or that it will actually improve anything since my DVD playback is so crappy. Now I use my regular TV with built in DVD since it is SOO Much better.

Also, I bought a DVI monster cable but then found out that my cable company (CHarter) does not transmit through it although there is an output on the receiver because of possible copy protection issues. Will I ever be able to use the DVI? How about if I change cable companies?