Get the 6412 DVR...you'll be more than satisfied.
Secondly, re: the transition from dvi to hdmi...well here is what I have found:
a) Fortunately I live near 5/6 high end audio/video retailers. Their input for me was this -- stick with component. Several indicated that on my display (Sony LCD RPTV 42) that I would not recognize a change in PQ between component and hdmi. And that to see such a difference a few indicated that I would have to have a 1080p projector. Additionally, many further suggested that beyond a very hind end video use, hdmi was simply another effort by content distributors to copy protect their content, i.e., totally worthless for the average user.
b) I purchased a $75 hdmi cable the day I got my phase iii stb from Comcast. Plugged it in and sure enough did not see a discernable PQ change watching either a network HD program nor Monday Night Football. I promptly took the cable back.
Plus, I couldn't figure out why I would need an hdmi cable anyway since I was not taking both the video and audio signal from the 6412 to a single unit that would then send the video to the display and play the audio track.
Get the phase iii stb and use component cable to the tv and optical your tv or your home theatre system.