I completely agree with the M60 EP500 combo to go along with the 7300. I know you're on a budget, but I wouldn't skimp on power. A room that size is going to require adequate power to push your speakers.
As for convincing your wife, just be honest and tell here it'll be a better movie watching experience for both of you. She'll be less likely to have a problem with it when she's enjoying a movie she likes in your new home theater. Also, be sure to do something nice for her (massage, day spa, etc.).
