Roger, thanks for the clarification- my apologies for getting a little defensive; I sometimes can't see past the amount of effort I'm putting into this- and can certainly be myopic. Since I already do something similar for the FFT measurement in SMAART, it shouldn't be a big deal to trace the electrical output. I guess the Center channel is as good as any to test.
Jeff, if what you have literally follows Amir's drawings, then the issue is modal- and Trinnov can't fix physics. Amir's rendering shows a classical Axial mode build-up; looks like the fist axial mode for length coupled with the first axial mode for width. The placement of the 2 subs on the back wall could have just as easily been on the front wall- and the sub in the ceiling is a great idea for when you can't build into walls! That 3rd woofer is where the magic is happening: it's located in the first axial mode for width, so it negates the null- then by being what looks to be roughly 25% off the front wall, it fills in the null of the second axial mode for length- and so you see the depression placed evenly from side-wall to side-wall (I'm sure those aren't the only modes present, just the most egregious). Realize that before EQ, that's still a 20 db depression.
Trinnov will do what it can to optimize for seating location, we can certainly create a preset for that particular seat, and that can be recalled by the Rhapsody when the 2 are connected. BUT....If that depression is caused by a null, the only way to fix it is to fill it.
If I remember pictures of the addition correctly, you have attic above the theater, right? Like Art's theater? If so, you can probably locate at least one woofer up there (several) and shoot them through grilles (HVAC). Otherwise, JL makes a very thin driver 13" woof, that might fit the bill for under your chairs (placed throughout as well). There are lots of things that can be done. I would start with the TEQ, only because you've expressed the desire for the other channels to be optimized that way anyway. If you can't get the results you're after with just the TEQ, then add subs- you have 4 extra channels that you can play with, I can do quite a bit with 4 channels and some woofers
It seems that you're fully aware that you need more woofers anyway.
As a side note: this exact issue is why there are 8 subs in my room: the 2 18"s in the front do the heavy lifting, the front-most pair of 12"s help reinforce the main LR speakers, and the second and third pairs of 12"s are strictly filling nulls. Is the bass in my room perfect- no, but variations from seat to seat are extremely slight, and row to row are slightly noticeable (in the end, I have to tune the room for the money seats). The benefits I glean from so many woofers: headroom, it's much easier to achieve high SPL with so many woofers- and the amps hardly work for it, same with the drivers- you barely have to move them to get the desired effect. Tautness: because the room is essentially "actively" treated for bass, there is little to now overhang on bass notes- regardless of the seating position: this is especially important in a scene like the sniper fight in Hurt Locker; the concussion from a Barret does not linger, the projectile leaves the barrel and the concussion is gone.
Noah, I'm not sure if I would call it "salt and pepper" on the phase target curve, probably more likely that you could adjust the phase response through the crossover regions, to correct for the rotations of various filters. I noticed that last night after optimizing my second preset; the bass from a bass guitar and drums, etc. sounded like it came from the mains (crossed over by bass management at 92...to the 18"s) that was nice, I like that it makes them sound like full range mains.
Amir, those renderings are super-cool! Does Keith use CATT? I tried that software years ago, but never had the processor horsepower to do it right.
A note should also be made that the before condition is a sub located in a tri-corner- the absolute worst place for a single sub, because it excites all modes to their worst levels.