[harsh]

I currently have two Dish 500 dishes, one for the 721 and the other for the other three receivers. Can I put a Quad head on the 721 Dish 500 to share with the 622 (for 110,119) and add either a Dish 300 or Dish 500 pointed to 129 for the 622? I'm thinking this would give me better alignment capabilities than one Dish 1000 pointing to all three.

There a couple of "issues" that you need to be aware of:

1. I'm pretty sure you can have up to six tuners on an account. One of your existing receivers may have to go.
2. The ViP622 and 721 are going to work a whole lot easier if you replace the 721 dish with a Dish1000. In this way, you can avoid running any extra wire inside the house.