My room size is similar to yours and I just ordered my HTIB. My choices were between the Onkyo HT-S7300 and the Denon DHT-591BA. Both really close to $600 on Amazon. The Onkyo is 7.1 and the Denon is 5.1.
From what I read, to get the benefit from the 7.1 you need to be able to place the rear speakers BEHIND your listening area. This means if your seating area is against the wall (like mine) you won't be able to take full advantage of the 7.1 setup. That on top of multiple reports of the Onkyo running hot led me to the Denon. I have a feeling the Boston Acoustics speakers will sound a little better than Onkyo's as well, but I have no proof of that.
That's the best I can do to help you
. Good luck with which ever way you decide to go. I'd go to Google shopping, Best Buy's website, and Amazon.com and read the reviews for anything you're interested in. Don't forget to search these forums too!