Wireless TV Interface

Doesn't the Tivo have to be at the point where there is cable, ie the closet? And then Tivo connects to the TV via HDMI, so I don't see how that solves anything?

As long as there is room to be able to crawl, doesn't sound so bad to me. For a limited operation like that you can just support yourself joist to joist. Or get a length of plywood, lay it across. The insulation on top makes it a little more difficult, I'm assuming that is extra that was added on top. If so, you can probably just roll it back, do the work, put it back. You already have the holes drilled for the existing cables. Should be pretty straightforward.

If you don't have stereo, its 2 and 4.

Then, it could be (but probably isn't) composite video and an optical audio cable.

Make sure the wood you place across the joists Can support your weight. It's no fun if it breaks while you Are standing on it. Don't ask me how I know this.

I made up some 1x12s with cleats that lock into the truss chords. (26" long with the cleats at 22.5"). Those are easy to move around in areas that do not have nailed in flooring and you can slide one out in front of you, pull the trailing one behind if you are in a very low part of the attic. We have 2:12s and 3:12s here that are only 4 or 5' high at the peak.