@jimmy_jet, your post brings up a few different matters:
1- The Fletcher Munson Curve Erik alluded to (Google it for info).
2- The power requirements of the MG3.7i. Highly dependent upon room size and acoustic properties (diffusion preferable to absorption, typical with planars), preferred SPL listening levels, etc. In case you don’t know, Roger Sanders created two different versions of his amplifier, one for magnetic-planars, the other for ESL’s.
3- The property of the Magneplanar loudspeakers with which you have recently become aware: the "Maggie mist". That phrase was coined in the 1970’s in the pages of The Absolute Sound, and refers to the tendencies of Magneplanars to sound veiled and lifeless until a "certain" SPL has been reached.
Some attribute the mist to the very low sensitivity of Maggies, but I myself am dubious. The Eminent Technology LFT-8b is of approximately the same sensitivity as the MG3.7i, yet does not exhibit veiling at low SPL. Others attribute it to the moving mass added to the Maggie m-p drivers by the conductive wires glued onto the Mylar (the ET LFT driver has it’s very low mass conductive traces vapor-deposited onto the Mylar), still others to their single-ended design (the 20.7i and 30.7 have push-pull m-p drivers, as does the ET LFT midrange driver. All three loudspeakers have true ribbon tweeters).
Whatever the cause, the Maggie mist is something you will need to learn to live with, as it is incurable (certainly not by an amplifier). All speakers have flaws, the trick is in finding one whose flaws you can live with. If you haven’t done so already, I suggest auditioning an ESL or two. They provide many of the virtues of Maggies, without some of it’s flaws. But then, they too have their imperfections. Pick yer poison!