I'm curious about how you have the sub set up. I've never gotten a sub to sound right with Maggies. Are you using an external Xover? Or does your amp provide bass management?
First, I have very small, very fast subs. They're the now discontinued Mirage MM8s, but the identical unit lives on as the Energy ESW-M8
. For speed and clarity, they have aluminum cones, a very supple, linear, and long-excursion surround, and lots of power--360 RMS/1200 peak.
They are line level input only and can accept a stereo or mono signal. I have a pair working left and right, and positioned close to their respective main speakers. This keeps the L-R bass fundamentals in sync with the panel's upper bass and overtones regardless of where your position in the room.
These subs also have a pretty comprehensive set of controls for blending--volume (of course), 0-360 deg. continuous phase control, and continuous crossover control from 50-200 Hz or even bypass.
I don't try to do too much with these subs. They don't go deep or loud; just to about 36 Hz and 106 dB. I don't use a high pass Xover either. Basically I use them to augment the same 40-60Hz range as Magnepan's own DWM, help pressurize larger rooms, and fill in where the Maggies start rolling off so they're flatter in the 36-60 Hz range.
And it's a lot easier to blend an 8" high powered, light-diaphragm sub with 1.7s than trying it with a single 12" or 15" sub reaching down to 20 Hz.