Oh yeah, there won't be an RF output on the 622 or 722 for TV1, so you'll have to use some sort of HD cabling to mirror downstairs, and since TV2 isn't HD, I don't see why you can't use coax with regular F connectors. AV would be a little better picture, but having RG-6 ran to those locations wouldn't hurt. I would still junction all the cable in one spot and install any splitters for the backfeed there, and run two lines from the Dish location. I don't know why you'd want all those cables terminating right by the plasma, but it'll work I guess. Installers do carry diplexers and splitters, and usually have some method for tracing lines. All we really need is the cable ran. Running back and forth across an attic chasing lines and splitters, etc. is a pain.
Just to be clear, you don't NEED two lines coming from the Dish, if you are just getting one DVR, but I like to think ahead. Just my opinion.