The only way a theater couldn't turn it up would be if the feed's dB level was just too low. They could "turn it up" definitely, but it just wouldn't go much louder.
*edit* Try this: if you have variable control of your speakers, play some music. Turn the volume down fairly low on the program that you're using. Almost inaudible. Then turn up your speakers and see how much of a difference it makes in volume. It won't be drastic.