I have a 40'L x 16'W x 13"H RV garage that I want to set up as a game room/theatre. CANT WAIT!!! Whats the best way to set up the speakers with so much room??
That is 8320 cu.ft! What is your budget? Does the ceiling need treatment and the ceiling lowered to put insulation above the ceiling?
That is going to take a big powerful system to fit that space. You won't get spine tingling SPLs with a receiver and pipsqueak speakers. This will take serious equipment. I would try and organize a mechanical chase, so you can get behind the equipment.
I would go 7.1 in that room. Unless you build big back loaded horns, you are going to need serious amplification. I agree with using an acoustically transparent screen with speakers, preferably huge ones, behind the screen.
A project like that really makes me salivate. In that room custom DIY speakers will pay dividends in terms of results achieved. To do the job well in a space like that will take a serious cash, time and sweat equity investment.