My experience adding subwoofers to 2 channel

Tim No, Right now I have modded out Acoustat 2+2s. Quads are not linear arrays. Full range linear arrays have to extend from the floor to the ceiling. I am on the brink of getting SoundLabs Majestics 845s as I have 8 foot ceilings. Between the speakers is a theater screen. The sub drivers are front firing. The inner two actually face each other with three feet between them. This gets the driver closely coupled to the front wall. 
The outer subs are against the side walls facing forward. Their drivers are closely coupled to the side walls. The main speakers are angled towards the listening position. A line extending through the sides of the speakers will intersect the faces of both subs on its side.
Your Maggies are linear arrays down to about 150 Hz where they convert to point source. In order to get the full linear array effect you would have to cross to the subs no lower than 150 Hz. But then your subs would have to be closer together, about 3 feet. I wish Maggie would make a speaker with 8 foot woofers. It would make life much easier.
I hope your listening position is not right against the wall. If it is move it forward a couple of feet. Sound waves are very slow. You have two subs back there with you and you hear those fractionally before you hear the ones on the front wall. This will smear transients. You want to hear all your subs at exactly the same time. You also have dipoles so you want all your sub drivers in the null zone beside each speaker. If your TV is mounted on the wall up off the floor you can put two woofers between the Maggies facing each other right up against the wall under the TV. Now If you try crossing at 150 Hz the subs will have to be no farther apart than three feet. So you would array them across the front wall and up the side walls three feet apart.You do not want to put a sub behind the Maggie. It will cause weird interactions with the woofer panel which is why I locate them in the null zone. With your woofers 3 feet apart they will all act as one driver and you will hear all of them at the same time. If you move them further apart and cross lower, 100 Hz cross puts the subs 5 feet apart you will have a very important segment of the bass drop into point source mode and that segments volume will drop off rapidly as you move away from the speakers. I wish Maggie would make their big speakers 8 feet tall, actually 7' 10".
The room is 16 X 60 feet sort off. The system spends much more time playing music but it does TV and Theater duty. I have no need for rear speakers or a center channel. I have a digital preamp which includes room control and the best bass management ever made. I can adjust cross over points and slopes on the fly. I have up to 10th order slopes and the cross overs can be adjusted in 1 Hz increments. I also have complete control over levels. Thus I only need passive subs and I am much happier choosing my own amps. The only unit that comes close is the Trinnov Amethyst. There are stand alone digital bass management systems out there. I believe DBx makes one. Sanders uses it in his speakers. There's another one who refuses to make his speakers taller. Talking about bad recording engineering. I was just listening to Neil Young's Harvest. The snare drum is right in your face and Neil and his guitars are like 50 feet behind. Pretty surreal.

Sub integration for proper bass is not the way...
Note the word proper.

Change your speakers or accept them for what they are.

Jmac:

I have been using a HSU ULS -15 MK2 , doing double duty for music and HT, for about a year. I find it very well built and performs very well. With all the talk of multiple subs I am tempted to get another one to see how much better it could be, but so far every time I think it out loud, the wife gives a bad reaction. But you know what they say, its easier to get forgiveness than permission, so one day it might just apare.

Hello mijostyn,

    Thanks for the clarifications on your system. I know 'ESL' is usually an acronym for electrostatic loudspeaker but mistakenly thought the Acoustat 2 + 2 were planar-magnetic speakers. I now understand they're ESLs with the '2 + 2' designating there are two 94" tall panels utilized for each channel, meaning they're technically not a pair of speakers but a quartet of speakers. My mistake.
     Ever since I bought my 2.7QRs used about 2001 I've been experimenting with single and dual subs in an attempt to incorporate good bass response and impact in the 20-35 Hz range I knew they were lacking.  After a lot of research and some luck, this led to my learning of the 4-sub distributed bass array (DBA) concept and buying the Audio Kinesis Debra 4-sub DBA system on a trial basis about 4 yrs ago.        
      My current thinking is that this DBA system has provided such accurate, detailed, smooth, natural, dynamic and extended bass down to being flat at 20 Hz while also seamlessly integrating with the quality and speed of my planar speakers in my room, that I honestly feel very fortunate to have this high a level of bass quality in my system.
      I realize, however, that a linear bass array sub configuration could provide even better bass performance in my system and room than my distributed bass array.  
      I'm hesitant to find out, though, for several reasons. I have a much better comfort level with the distributed array concept due to a better understanding of the physics and psycho acoustics involved than I do with the linear array concept, the distributed array is already completely hooked up and working extremely well and my wife and I are also very pleased that the 4 subs in my room are currently so physically inconspicuous and well integrated into our combination living, music and ht room.  In addition, it would likely take a large room rearrangement just to give the linear bass array a try and there's no guarantee I would prefer it either.
     I wanted to respond to your questions and suggestions from your last post, too.  My listening chair is backed up to and centered along my room's 16' rear wall.  But I move it about 3 feet out into the room for serious and prolonged listening sessions for better soundstage imaging. My panels are always a minimum of 3 feet and sometimes more away from the pair of subs behind them.  Both sub 10" drivers are also facing the front wall and not directly into the back of these panels.  I notice no detrimental effect in any frequency range from this positioning.
     You also stated: "You have two subs back there with you and you hear those fractionally before you hear the ones on the front wall. This will smear transients. You want to hear all your subs at exactly the same time."  
     It's my understanding that the time-domain on frequencies under 100 Hz are not as critical as some believe.  I also read an article on an experiment proving we don't even detect deep bass sounds until the entire frequency soundwave cycle exists in the room.  The experiment consisted of subjects wearing headphones.  A series of computer generated  partial and full cycle deep bass tone soundwaves were played and the subjects only were able to detect the bass tones in which the full cycle was played and no sound at all when the partial cycles were played.  As you know, it takes some time and distance for a full 56 foot long 20 Hz soundwave to develop in a 23 x16 foot room.

Tim 
      

I have used a tri-amped electronically crossed three way line array system that I built myself.  This worked seamlessly.  The 12 inch woofers worked well as subs essentially running 32- 250 hz.

I am currently building a new system to go downstairs(sine my wife commandeered the other one for watching movies upstairs).

This one will be a Quad amped electronically crossed  line array: per side:  15 ribbon tweeters, 25- 2 inch midranges, one 8 inch mid woofer, and one 12 inch sub woofer.  

Electronic crossovers(digital or analog) are the key to making this work, IMO.