I agree with John, 1k is pretty much the minimum: you definitely want a sub that will give you a theater feel, and 11'x20' is a decent sized room. A 10" sub might struggle there so don't worry about overkill. Drop a line to the people at SVS for recommendations if you haven't done so already. They thought a powered cylinder would work best in my room, and I did continue shopping but eventually went with their advice. The box subs for the bass I wanted were huge. Once your girlfriend hears your quality, finely tuned setup she'll see the investment is worth every penny. Word of caution; you may not want to frequent movie theaters very much after the install - but then you won't have to...
