I just did a quick Google search, but couldn’t find any reviews or tech info on that Magnepan.
I took a quick look at 3 different Magnepan reviews on Stereophile. It seems all 3 speakers had a sensitive of about 83.5 - 85 dB/w/m and minimum impedance of about 3 ohms 20Hz-20kHz.
According to this calculation, 100W would produce 100dB SPL from 10FT distance if speakers have 83.5dB/w/m sensitivity.
http://myhometheater.homestead.com/splcalculator.html
According to AVTech measurements, a Denon AVR 3805 receiver can produce 170 watts into 1 ohms.
AVTech Miller Audio Research Lab Results
Denon 3805:
Dynamic Power Output into 1 ohms: 170W (1%THD)
http://www.milleraudioresearch.com/download/reports/aug04/denonavr3805.html