What we have been installing on zone systems with smaller zones is a controller (by Jackson Systems) that will partially open closed zone dampers in response to an adjustable duct static pressure control. We will have the smallest zone calling (only) and adjust the controller by air noise in that zone. So far we have not had any complaints of overheating or over- cooling any zones. We have installed these controllers on different zone systems all you really need is 3-wire zone damper motors. It also will work on anybody's unit single or dual capacity.
Mike Hadley CGD CGI