Distributed Bass Array configuration

Please correct me if any of my comments here are incorrect as I don't claim to have any expertise. I do believe you are misinterpreting the  "term" - "stereo subwoofers". It is a "term" not a sonic phenomena or an implementation in any recording process . I do believe it was originally  meant as the description of using 2 subs on receiver/pre amp as 2 separate channels so not to not to be confused with 2 sub outputs running parallel. Although this is a 2 channel discussion listening subject  I do believe the whole concept began with surround sound and then was deemed profitable for 2 channel listening. So, when a surround sound mix is configured for a movie the "LFE" channel is single and mono ( as is every channel / speaker ), it does not have a left sub mix and a right sub mix, much less a 4 sub mix, it is a single signal. Then the receiver through it's processor separates it to a left channel and a right channel so the mic calibration processing then allows for different volume levels to be "matched" at the listener position. Now recent implementations of Audyssey and definitely Dirac LIve may incorporate separate phase shift and delay but it all comes from a single mono signal being manipulated to create a "means to an end".
Again correct me but isn't "stereo" in itself just taking a recording from multiple "mono" microphones and then an engineer manipulating all the separate mic channels into a "stereo mix" in an effort to create a "perceivable" soundstage again as a means to an end ? I think we should use the term multiple.
I listen to Paul McGowen on Youtube ( maybe the meaning of stereo subs is a good question to send in ) and consider him quite informative but don't take all he says as undeniable truth. Actually, I believe he has mentioned that the owner of Audioquest is a friend of his and I heard that guy the other day on YouTube say that power regenerators are useless ( and a great amount of Paul's expertise and companies monetary value is based on that very component ) so I guess even his friend and also an "expert" doesn't agree with him. I might mention that his company is often criticized as not legit in the premises that their products are based on . So who are the experts? 
But let me conclude in complete agreeance that we can't discern the location of the lowest frequencies, it's just a fact. Our ears/brain don't work that way for a reason. In real world circumstances there is no practical use for "hearing" those frequencies. One main component of hearing and discerning placement is to realize where danger may be coming from and if your in danger from something creating sub harmonic frequencies it's probably an earthquake and you ain't getting away from that.

Seems that the term non- directional is getting mis-interpreted also. The low frequency sound waves from a subwoofer emanate in all directions and although seemingly an oxymoron is called non-directional because of that fact. As opposed to high frequencies that emanate from a tweeter in a single and focused direction.

Tim ( noble101), yes, it does get better as you add subs. I couldn’t believe how much improvement there was adding a third sub after already getting the improvement of adding a second. My front subs have to go to the inside of the mains because there is an opening to the entryway on the right and an opening to a hallway and a sitting room beyond that on the left. Open floor plan and basically no corners either in the front. So that may be one reason for a dramatic improvement of the third. Don’t know if I’ll add a fourth.

MAPMAN -
It definitely does not get better because there is more. These guys you see on YouTube ( some considered influencers ) with multiple subs primarily in their theater systems are going for more bass and sound pressure. I guess if you just want to impress people by making their bowels move and shock the crap out of them ( pun 👍 ) go ahead and get your kicks that way.
You’re not getting more  bass if you have set things correctly. You can get more if you don't mind it being out of balance with the upper end but that’s not the way I listen to music or movies for that matter.
What has happened for me ( doesn’t mean it’s going to be exactly the same for anyone else in their room/configuration ) is that with two subs there was better blending ( horizontally ) without the perceived location issue derived from one sub. But, then the bass ( especially kick drums ) were overly emphasized and got just so centered that it was almost the only spot many of the lower frequencies were being placed. Unfortunately I have to set my front subs to the inside of my mains ( no choice ) so that influences the issue.
But when I added a third sub, wow!! Game changer and now I’m elated. The low frequencies are completely balanced in every way with the rest of the music ( frequencies ). There is absolutely no sensation that there are subwoofers ( external speakers from the mains ) and the bass is just part of the music ( heavenly ). The bass is still centered ( that’s the way it was mixed by the engineer ) but it spreads further horizontally and very naturally ( as I would perceive natural ). It fills the listening area ( I’m not saying there is bass all over the room ), making  it smooth with no overemphasis anywhere. I feel the subharmonics without it feeling like they are ”hitting” me ( even with movies ). Not that it’s due to multiple subs but I’m relaying that you don’t get that type of issue because you have added multiple subs. I think there can be that perception from the hype of the bass centric crowd.
What amazes me is that the third sub is less than six feet ( behind me ) from my listening position and I don’t “feel” it even at higher volumes, it blends sonically invisible.
None of this would be possible to achieve setting up by ear ( well maybe with a couple of years of trial and error ). It’s only been possible with the implementation of the MiniDSP HD 2x4 and REW.  The full use of REW with its eq section ( room correction with parametric eq that is similar to Dirac ). Beyond that the MiniDSP offers delay options so after the REW eq you can make tone sweeps and see which delays ( or lack thereof ) on each sub is most beneficial ( or not ). This is the best $315 I’ve ever spent!! Sometimes technology truly is your friend.
Now there is quite a learning curve and definitely trial and error but it is more than worth it!! Some may consider themselves to already have achieved this but I’m confident that if you implemented the MiniDSP you would achieve even further benefits and results.