My first thought would be five M3s. I ran my last system with three M3s across the front...and two "Brand X" in the back...with real good luck. The three M3s across the front were just great for perfect scans and pans and they went low enough that a sub wasen't really needed(but actually wanted)but it made a very useable 5.1 in a 3100 cu ft room. And it sounded great for tunes too!
Rich.