I installed a Fantech FG6 in the equipment room outside of my theater. I use this to draw air out of the room when I am in the theater. The fan dumps the air into the return. I use a variable switch to control the speed of the fan.
My room is sealed rather well and I have three 6" outlets in the room and one large return. I use the fan on this return to boost the amount of air pulled from the room.
Now, I DO have an issue with the room warming up when there are 4 or 5 adults watching a movie, even with the fan running. The issue comes from the fact that the basement and first floor share one HVAC system. When the room fills up, I need to run the AC to cool it. This causes the first floor to become really chilly.
To solve this, I'm looking to install a minisplit in the theater to provide cooling, paricularly in the winter. If I were building again, I'd install a separate HVAC zone for the basement. That way I'd have full control of the temperature in the basement, separate from the rest of the house.
The take away here is don't underestimate the need for cooling in the theater, even in the winter.