Tis a dilemma I too have faced. In my case the room is about 14x13 with a eight foot ceiling. From the sound perspective, the folks from the speaker maker susgested the smaller space.As the amp, a tube one, would not have to work as hard. The big issue is really one of family lifestyle. Do you want a room dedicated to music and movies alone or one that will bring in the future pool table and such. You mentioned a former remodel job,consider moving such things as water heaters etc that may be in the wrong location for your needs. Douglas puts some very good points for anyone looking to do this project. Main thing is try to get it right the first time no matter how long it takes, once done you may have little chance to go back and change the configuration. Good Luck
Glen
Glen