Role of sub woofers?

You have just discovered what many of us have been saying for some time now, that more subs is better, and not only for bass but for imaging, and making the whole system disappear. 

This happens because bass is so much different than midrange and treble. With bass the waves are all much longer than the room. So they cancel and reinforce creating peaks and nulls. You try and smooth it out with EQ, all you do is make them worse. Better at one point but worse everywhere else.

More subs in more different locations means more peaks and nulls. But more subs also means each one can be run at a lower volume so the peaks and nulls are smaller and the overall result is much, much smoother.  

The next improvement will be to move those subs so they are not symmetrical. Symmetry is the enemy of bass, as it aggravates the reinforcement/cancellation effect. When adding the third put it likewise on a different wall and a different distance from the corner than the others. 

My system is like this only with 5 subs and the subs and the system entirely disappears, the room dissolves, you are immersed in the sound field, and the bass is freaking to die for.

https://systems.audiogon.com/systems/8367

Search DBA, distributed bass array, Swarm subwoofer system, etc.

So may audiophiles report exactly the same thing.  They try using a sub only for the lowest octave for purity's sake and then are amazed at the improvement when they turn the high-pass filter up to 80-ish.

Imo the best thing you can do for a system is use subs with a high pass crossover (like JL CR-1) to the mains. I wish more preamps had bass management in them. It could really cut down on the clutter. 
I have found most speakers cross over best at 60hz give or take. Not low passed but crossed over. If you are going to just low pass the subs they need to come in under the speakers. I like to be 1/2 octave  above the minimum motion of the mains bass driver if using a 24 dB slope.  
60z is good because a lot of bass drivers start to roll off around 60hz. 

db, do you have the Velodyne SMS-1 Manual, Sweep Tone CD, calibrated microphone, and the Windows Setup Program loaded?

This is the Outlaw SMS-1 Manual which offers an alternately worded explanation of the Velodyne Manual which you may find helpful in explaining how to use the SMS-1. http://pdf.outlawaudio.com/outlaw/docs/sms1guide.pdf

I have both SMS-1 manuals, several sweep tone CDs, calibrated microphone with stand, and a monitor for displaying the various videos generated by the SMS-1.  I prefer the Outlaw manual.  I actually have three SMS-1s, but use only one.  An Ayre KX-5 Twenty preamp connects to the input of the SMS-1.  I've tried a couple of high-pass crossovers between the KX-5 and VX-5 amp even though Charles Hansen discouraged it, but it turned out he was right; the sense of openness was compromised.

db