I made a couple of phone calls and found out that both Aprilaire and RCS make a 4 zone controller that will work in conjunction with my HAI OmniPro II automation panel. The way it would work is that the OmniPro II can control up to 64 thermostats (this will allow me room for future expansion
). So I would have one thermostat for each zone (like any other zoned system). The Omnipro would control each thermostat (setting hi/low temp, etc) and the zone controller would then operate the dampers based on the thermostats request for heating/cooling. All of this functions as I had hoped.
The more complicated part is the back pressure. They sell a motorized static pressure controlled damper that is placed between the supply trunk and the air return trunk. If too much pressure is building in the supply trunk, the system will open the valve in the pressure release duct and allow the excess air to flow back through the system without building up pressure. The trick is to properly calculate what size bypass is necessary for your system based on the smallest zone. Both places told me that if done properly, the theater could in theory be on its own zone. With only one 8" duct feeding a single zone. They thought I would need at least a 20" bypass. I will need to do some math on the size of the supply trunk and the amount of air provided by my system. I will probably have to have some help with that to make sure it is right.
Knowing all of this, I think I am headed down the right path to designing a system that will benefit the whole house - not just the theater. Mario mentioned that his system is able to pull in cold air from outside during the winter. I mentioned to one of the suppliers I talked to that it would be nice to switch over to exterior air to cool the theater during the colder months. They mentioned that this could be done using my existing outside air temp sensor (to determine if the outside air is cooler) and writing some code to switch off the zone and turn on some form of inline fan to pull air in from the outside. I am going to need to look into this further.
Once I have further detail around cost and functionality, I will post the information. If the cost is too high, it may be better to skip the DIY route and look at having someone else install the system. On the hand, that would take all the fun out of it