I agree with mdrew although I won't go as far as to say this is a design issue. It could be a manufacturing issue. We just don't know.

MadScientist's graph suggestion is a good idea but it's impossible to understand the graphs without understanding the test procedure and equipment used. And this is where things get very complicated and require careful study.

For what it's worth, here is the performance that I am experiencing with my M80s in my very bright, 4000 cubic foot space. The voltage is measured with a $30, analog meter from radio shack that has no specs whatsoever. I am confident SPL is accurate to within +/- 1 dB for this frequency. I only went up to -10 on my amp's gain because I was worried about damaging a driver.

Both channel levels are set to 0, left channel RMS voltage measured with a 1 KHz tone (the test CD says that this is a 0dB tone; all other tones on the CD are -10dB). SPL is C-weighted, slow with two channels from 12 feet away. The impedance (Ohms) was taken from the Axiom graph that Randy posted. Power is in watts for my left channel. The power for both channels is of course double the power for a single channel. My Denon amp is rated 90WRMS + 90WRMS for 8 Ohms with 0.08% THD (over audible frequency range) and 125WRMS + 125WRMS for 6 Ohms with 0.7% THD at 1 KHz. No rating is given for 4 Ohms. Based on the 1 KHz input frequency, the M80s are operating at 8 Ohms.

amp.....Vac.....Z......Power.....SPL
-30......0.9....8.5......0.1.........75
-20..... 2.5....8.5......0.7.........84
-10..... 9.5....8.5......11..........92

I haven't spent any time interpreting these results to understand if they "make sense" or how the apply to Randy's situation. Comments from anyone?