Tuning multiple channels

Using an extender and two HDMI inputs on your HDTV will accomplish this.

Depends on what kind of tuner. If you are talking about a CableCard tuner, then no, the only way is to use Media Center, and that can only "watch" one tuner at a time. You would have to actually set the other tuner to record the other show, it's not constantly recording both tuners like a typical cable box does.

If you are talking about an ATSC or QAM tuner, you may be able to use two different TV programs at once. For example, my Hauppauge card came with it's own WinTV program, I could use that with one tuner, and WMC with the other.

In a word no. Go back to TWC boxes if that feature is a deal breaker. I can live without esoteric uses such as you mentioned.

You aren't using a DVR correctly.

Just how do you think you're able to rewind "live" TV if it's not being recorded? Your DVR probably has a buffer that's constantly being updated with recorded content. If you have two programs that you want to switch back and forth between, simply record each one and switch back and forth between them. I do this all the time in WMC when there are multiple football games I want to watch. I'll watch one game for a while and then stop it. I'll then start playback of the other game and do the same. I generally try to watch it in short spurts, usually during one team's complete possession of the ball, so I don't accidentally see a score update for the other game being shown at the bottom of the screen. This way I can keep relatively current with each game and still be able to skip past all of the commercials.