While I in no way consider myself in the same class of expertise as some of the respondents, I would suggest a look at Legacy Audio. Legacy is not as exotic as most of the suggestions here; But I heard the newest version of the Whispers at CES 2 years ago. The only speaker I liked better was the Anat Studio II, which is exponentially more expensive. I have a similar size room. I use two Legacy Focus and the sound really is unbelievable. I have a bit more power available in my amp which may help; But the New Whispers come with built in dual 500 watt Amps powering four 15 inch drivers each side. The extra power and piston area will surely go along way toward filling a large room. They are also very efficient. Have fun designing!
http://www.legacyaudio.com/products/view/whisper-xd/
http://www.legacyaudio.com/products/view/whisper-xd/