For the utmost in control of your HVAC zones, try using modulating dampers.
Modulating dampers feature connections for both opening and closing the damper, allowing variable closure of the damper. The dampers feature Open. Close, and Common 24VAC connections. By supplying power to the appropriate connection, you activate the motor on the damper, opening or closing the blade for 100% flow or up to 99% closure.
These dampers can also be used in "two-position" operation, moving to fully opened or fully closed, and are constructed with a unique design that ensures it will staty round even with the roughest installation.
The RDM-series of dampers is available in 6", 8", 10", 12", 14" and 18" models, with normally open and nomrally closed options.