Marantz SR-7010 rated power consumption is 710 watts (I assume RMS).
Assuming I can get 60 watts per channel RMS with all nine channels driven. 60 x 9 = 630 watts. So that's pushing the limits of credibility, assuming 90% of the power in gets converted into power out.
So assuming with all 9 internally amplified channels going full tilt, and with an extra two channels also going full tilt, and assuming an average 10 foot separation between speakers and ears, I get a calculated 106.5 decibels. Which is somewhere between a newspaper printing press and an airliner passing overhead at 1000 feet (i.e. effing loud).
At 50 watts per channel I still get 105.7 dB and at 40 watts 104.7 dB. 80 watts per channel gives an imperceptably small increase to 107.8 decibels. So, as I said, 30 watts per channel doesn't do much.
If I used, say, a pair of Emotiva XPA-Gen 3 7-channel modular power amps, 5 or 6 channels per box, I only get to 111.7 decibels (a 5.2 dB increase) with the rated 200 watts per channel all channels driven power output. That's quite a bit louder, granted, but not TWICE as loud.
To get to 116.5 decibels, or sounding "twice as loud" (which would be deafening, quite literally deafening) I would need 600 watts per channel.
This done using the calculator at:
http://myhometheater.homestead.com/splcalculator.html
And according to the scientists:
Exposure to sounds above 85 dB causes short term hearing losses called "temporary threshhold shifts". If these occur, your ears become less sensitive and sounds seem quieter than normal {hence you can't hear your mates on the way home from an Iron Maiden concert]. After some time, normal hhearing returns.
Repeated exposure to sounds that cause temporary threshhold shifts result in permanent damage to the ear in the form of a permanent threshhold shift. The ear loses sensitivity in the 3 kHz to 6 kHz range resulting in a "notch" in th ehearing range. Time of exposure is important, the louder the sound, the less exposure time before permanent damage sets in.
According to OSHA [the US version of the UK's HSE] are (A-rated, most HT measurements are C-rated, but you get the idea):
90 dB 8 hours
92 dB 6 hours
95 dB 4 hours
97 dB 3 hours
100 dB 2 hours
102 dB 1.5 hours
105 dB 1 hour
110 dB 30 minutes
115 dB less than 15 minutes
Now. I do accept that not all parts of a movie are really loud, but even so, think carefully before going for a "one point twenty one gigawatts" flux capacitor based amp!