I'm not sure if it would be less in a larger room. My room is twice the size of yours and I achieve 110 dB (C, slow) with peaks higher than that. Maybe it's because my room is very live and yours is more damped...I don't know. It's just occured to me though that my Denon may be cranking out more than your Yamaha. Although my Denon is rated 90W/channel into 8 Ohms, it's also rated 125W/channel into 6 Ohms and 170Wx2 channels into 4 Ohms dynamically.