So, I just had a Comcast tech over to set up Tivo on my DVR (I have a DCH3416 model).
He first had to make a call in and then the download process started. It took maybe 5-7 minutes to download and no adjustments were made to my signal strength, so I guess it was good to begin with.
1. It's pretty, though the Tivo sounds may get annoying after a while.
2. The install somehow reset the video formatting, so HD channels were coming in letterboxed. I had to go into the Tivio video settings to set it to 1080i Fixed, which appears to have resolved the problem.
3. So far, it seems as though the bug is still present, as I can't get DD5.1 on HD channels, even though I set it to pass through DD5.1 in one of the Tivo menu settings.
I'm going to play around with it a bit more and see what else I can break :-)