My digital channels and digital HD channels improved dramatically when I swapped HD cable boxes. I previously had a Scientific Atlanta HD XXXX (can't remember the exact model). I swapped it for a new PACE box that supported DVI (but I'm still using the component output, like before). The pixelization on non-HD digital channels went away. It also "upconverts" to either 480p, 720p or 1080i.
Enjoy,
TIC
Enjoy,
TIC