Muse, welcome. The first point is to disregard the advice of whoever told you to to avoid a Yamaha because of a possible "sharp" sound. Modern HT receivers are competently designed and none of them, including Yamaha, Denon and Onkyo, add an audible coloration to the sound when operated within their designed limits.
Next, as to a Denon recommendation, you haven't given a key piece of information: what is your listening distance? You've given a room dimension, but a room doesn't have to be "filled" with sound at the level needed at your listening position. Listening distance is far more significant than the variations in room sizes we find at home. I'd be glad to calculate your power requirements and suggest an appropriate Denon unit.
