I don't think I explained my idea well enough, so I'll add a drawing.
I'm working on zone one only, and have an unused zone available on the controller, and a spare wire available at both the controller and the manifold.
I want to isolate the new heads and have them be zone 8, w/o running a pipe back to the manifold.
In my scenario, I wire zone one and zone 8 to both open valve #1, which is in the manifold.
For zone 1 to continue to flow the same heads as it does now, the controller would open valve 1 and valve 8. Valve 8 would be wired to zone 1.
For the new zone 8 to flow, valve 1 and valve 9 would be open, and valve 9 would be wired to the available zone 8 on the controller.
So....
Zone 1 flowing - valve 1 and valve 8 open. Valve 9 closed.
Zone 8 flowing - valve 1 and valve 9 open. Valve 8 closed.
Thw wires to the two new valves would be a separate run - easily accomplished. I have an extra wire in the harness from the controller to the manifold to operate valve 1 using the zone 8 slot, which is currently unused.
I hope this makes sense. And thanks again for looking.
Al