The room size is 15 ft by 21 ft. I feel like R900 as the center speaker will be an overkill but it is recommended that LRC should be the same speakers if possible. Maybe I could use R600c and place them vertically? The sensitivity being 90 db I was considering using Denon 3313 with 125w (AirPlay is an absolute must). Is that enough power? I don't mind using another AV as long as it has AirPlay.