It depends on speaker efficiency, how far away you sit, and how reverberant the room is.
Dolby Reference level requires peaks of 105dB at the seats from the screen channels. Near-field, 1W would do this with 105dB/1W/1m horns; although in an acoustically dead room with seating 13' from 86dB/1W/1m efficient speakers you'd need 1000W.
Remember, the difference between 100W and 200W is only 3dB.
Dolby Reference level requires peaks of 105dB at the seats from the screen channels. Near-field, 1W would do this with 105dB/1W/1m horns; although in an acoustically dead room with seating 13' from 86dB/1W/1m efficient speakers you'd need 1000W.
Remember, the difference between 100W and 200W is only 3dB.