To give you an idea of what Nick and I are talking about, I just played a fire and brimstone scene from the Game of Thrones Blu-Ray using Dolby HD MA. For reference, I have my PS3 volume set to +4 (the max). I turned my Onk up to -10 which is simply ridiculous even for my large room and 14 foot MLP distance from the center. I would normally watch this scene at -25 which is thunderous enough. Anyway, I was measuring 7V peak RMS at the fronts and 27V peaks at the center. That's a four-fold difference in voltage and a 16-fold difference in power between the fronts and the center! That's like somewhere between 90 and 120 W peaks at the center!
Note this is pretty much at the rail limits of my Onk and I wouldn't doubt if I have some amp compression taking place because although it sounds loud, it doesn't sound great.
