Why do Maggies need a lot of power?

Maggies need power for the simple reason that they are low ohm speakers with an 86db sensitivity rating. The 1.6's are not as hard to drive as the 3.6's (the 3.6's dip to below 2 ohms in the bass). The combination of a low ohm speaker and a low sensativity (86db), means that these speakers are going to suck power from your amp to get volume. If you do not have an amp that is stable at low loads, this could be a problem.

You are right when you say current really matters in driving the Maggies. High current ensures low ohm stability and thus little possibility of clipping. High current amps double in power as ohms are cut in half.

I will say this. The Maggie 1.6's can be driven pretty by MUCH less low power than the Maggie 3.6's. I have heard 1.6's driven by an Audio Research CA50 50wpc (or so) tube integrated amp (great little integrated amp). The sound was pretty decent. HOWEVER, to really get the most out of Maggie speakers, more wattage and current will make all the difference in the world. I used to drive 3.6's with 665wpc and 50amps or so of ss current, and they sounded heavenly.

KF

Due to the dynamic nature of music, recorded peaks above the average power level required may climb past 10 dB's. In terms of amplifier power, 10 dB's is equivalent to 10 times the amount of power. As such, your calculations ( which i did not verify ) would mean that you would need AT LEAST 640 wpc in order to sustain said listening level and not have the amp go into compression i.e. clipping off the peaks.

Another variable is that sound does not travel uniformly through the air. Depending on the type of driver used ( horn, planar, etc.. ), the physical array ( front firing, dipole, bipole, line array, etc.. ), size of room and your listening distance, SPL's will vary accordingly. If you also factor in that most drivers DO go into compression when being pushed, you might be able to see that any "formula" for SPL's is "generic" unless you have a LOT of specific info about the installation.

If you look at the design of a Maggie ( or any other panel type speaker ), it is obvious that they can't produce a lot of driver "throw" or "excursion". Since it takes large excursions to move a lot of air ( both required for volume and / or low frequencies ), this type of design is limited in several aspects. Once you hit a given drive level, the power is converted more efficiently into heat than it is sound. As such, many engineers try to work within the "efficiency window" with these types of designs and limit low frequency response by using a dynamic driver for the bass and / or increasing the radiating surface area of the panel. Trying to get deep bass, high spl's and minimize compression / distortion is a very tough juggling act to do. That is why all but the largest speakers using a LOT of drivers are the only ones that can do it and do it well. Sean
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I had very good luck driving a pair of Magnepan MGIIIAs with two different versions of the B&K ST140 over the years.
The "original" ST140 was, as it's number implied, a 70 WPC amp with an iron core transformer. Not a lot of these were produced. Also used until recently, a later ST140, in which production swapped the transformer for a Toroid, increasing it's horsepower to 105 WPC.

I was able to achieve very satisfying listening levels in both large and small rooms with this setup. I do think that the combination of a lower impedence and sensitivity make amp choices of less than 200 WPC limited, but there are amps out there.

Make no mistake, The entire Magnepan line loves lots of good, CLEAN power. I never realized what the MGIIIA was capable of until I started feeding them a high power/ current amp. (Sunfire Signature).

Just my 2 cents...