Lowe's sells the Ideal compression tool for $20, and it comes with a handful of RG6 connectors. They also have a prep tool, I think it's about $7. Worth the investment if you ever plan on doing it again.
The existing dual grounding block isn't necessary if you're only feeding one 722, so you might just talk the installer into making the cables for you and using that block for your antenna, too, and just hand him the Jackson instead of the teenager at Lowe's.
Composite (yellow) isn't HD, but component (red, green, blue) is, up to 1080p and beyond with the right cable. The two reasons that everyone is going to HDMI are simplicity and expense; one 19-wire cable that carries both audio and video signals are a LOT cheaper than 5 coaxial wires with double-braided shielding and gold-plated connectors, and easier to run. In your situation, just to get the system up and running, invest in one long HDMI cable and use the Cheap-O component cables that come with the 722k for the living room TV. When you feel like it, get a better set of cables, which will cost about the same as an HDMI splitter, but doesn't require a wall wart for power.