My room is about 5000+ Cu Ft. My floorstanders and 2 Rel subs do a great job with a 65 wpc tube amp
I have done parking lots with 40 50K sq Ft with 4 PA speakers 15" w/ horns on top and a 1200 watt Crown amp that wasn't even at half volume. I don't even have half of the $30K into the whole PA system and my hifi speakers.