"gportiz" asked a good question, but no one seemed to answer it directly...
What gives a better picture? SD programming delivered to an HD TV in its native 480i or 480p signal (upscaled to 1080i/p at the TV), or sent to the HD TV as 1080i (having been upscaled to 1080i by the HD DVR)?
I'm sure the answer depends on the TV in question - Sony highlights a "Digital Reality Creation" ability in their modern XBR series that does sophisticated upscale to 1080p. Is this worth the money, or can a cheaper LCD with the HD-DVR+ sending 1080i look as good?
Summary question: how good is the 480i/SD signal to 1080i upscaling on the DirecTV HD-DVR - HR21-700 (or the HD-DVR HR20-700)?
Or, do most modern TVs do a better job filling their own screens with a 480i/p signal?
For most, I expect, the answer will be "try it both ways and see what you prefer". Too bad this is not much help in making a blind purchase decision...
Those of you with a modern 40"-50" XBR Sony LCD on DirecTV - can you all tell us if DRC-to-1080p from a 480i or 480p source looks noticeably better than SD programing coming from the DVR in 1080i (when you tell the HD DVR+ that your TV only supports 1080i).