I didn't mess around very much more with the setup, aside from having to retire my Maggies due to a crossover catastrophic failure on the Front Right speaker, so I put my Def Tech's back into service, and since I had to calibrate the speakers, I figured I'd tweak on the subs a bit as well...
I merely changed which port was plugged on the VTF-15, and re-visited the gain matching, and performed a bit more exact time alignment of the subs. The VTF is currently firing along the left wall, and I initially had the port away from the wall open; I plugged that port and unplugged the port closest to the wall. The resulting graph, unsmoothed, is not the best looking I've seen, but it sounds so good I've decided that unless I'm forced to change things, I'm calling it good. I watched a couple movies today, and listened to a bunch of music, and think this will definitely do.
A guy can only obsess so long on setup before it's time to listen instead of measure & tweak things.
I'm running the subs about 7dB hot on the very low end (healthy rising response starting at 120Hz, going to 30Hz), and it just plain sounds great. With the subs spread around the room, there is no localization of bass at all (not that I've ever found localization to be a problem with my HSU subs), the distortion is under 1% at any frequency I can actually hear (It creeps up to about 3% at 10Hz), when played back at my normal -15dB volume level.
I watched "BEQ" versions of 2 of my recent favorite movies for the quality of the sound design; John Wick 3, and Blade Runner 2047. At -15dB main volume for both, they showcased 2 very different flavors of bass. John Wick had chest thump galore on the gunshots, and BR2047 had crushing low and loud bass throughout. At no point in either movie did I ever detect a hint of distress from the subs. I honestly can't say that I could point out the location of the subwoofers if I didn't know where they were if I was blindfolded; lets be honest, it's hard to miss any of them visually as 2 are 4' tall cylinders, and the 3rd is a dorm fridge size box. But close my eyes and I hear bass coming from whatever speaker is supposed to produce it (in the case of John Wick), or just omnipresent as LFE in BR2047.
Listening to music, it's obvious I have subs, or very large speakers, but the bass comes entirely from the front (listening in stereo), despite 2 out of the 3 subs being behind me. Even with the house curve, drums sound tight.
I'm probably going to repair my Maggies' crossovers and set them up in a room upstairs. That's a project for later, as it means new amps, preamp, and sub to get for it... It never ends.
No! Try not... Do, or do not... There is no try.