It's not the frequency, it's the time.
Be prepared to take some time. Loosen up the sub for a few days by playing the radio while at work. Make some sketches of the controls and make several copies.
The Maggies are a very coherent LS, so the first focus should be alignment of the phase so the sound stage remains coherent.
There is no free lunch due to the laws of physics. Expecting woofer weighing several ounces to keep up with a tweeter weighing at most few grams is not realistic. The idea is to add the fundamental underpinnings to support the mains in a coherent manner. If the sub is too loud, the disparity in speed will be annoying.
The Force is flexible enough to ensure almost seamless integration, provided you take the time...
If you can get an assistant to help while you listen, the setup will go much faster.
First choose several source disks with substantial and diverse low end information : Large symphony with bass drum and tympani, jazz with acoustic bass, rock with real low end, not 100Hz hump, etc.
Select the sections for test listening and note them for easy access.
Set both xovers to ~50Hz, the phase to 90° and adjust the level so there is a slight to moderate increase in low end when the Force is on.
Each surface next to the Force increases the level at the expense of coherence and frequency comb filtering. If you can put it in the middle of the room, great. Coherence will be maximum, level will be minimum and my wife is leaving.
My Force ended up set in a corner about one foot from the side wall and 1.5 feet from the rear wall.
Now the fun begins.
Repeatedly play each selected segment listening for expansion of the low end while adjusting the phase control. When the phase is correct, the room will expand. You'll 'hear' the back wall behind the orchestra. On acoustic bass, the strings and the body will align. Kick drums in rock hit you in the solar plexus and you can 'see' where the beater is whacking the head.
Once the phase is correct, turn the xovers all the way down to 35Hz. Bring the level control up until there is apparent low end, but there is a 'hole' in the bottom. Drop the level back a bit and bring the xovers up until the hole fills in.
Now try dropping the A xover a bit and raising the B. The goal is to achieve as seamless an integration as possible. Level and phase adjustment may also be necessary. Tiny adjustments pay bigger dividends.
Once you've got it dialed, make notes of all the settings, room position, etc.
Depending on your level of neurosis, you may want to start again and see if you can make any improvement. Once my Force sub had played for about 30 days [about 100 hours], I started over and made a slight improvement on the coherence and blending to the mains. It's easier the second time around as you've become reacqainted with all 10 octaves.
Once you have it right, the increase in listening enjoyment is an order of magnitude greater than without the sub.
