Got room all re-arranged. TN's up front at 1/4 & 3/4 positions, and VTF's on rear wall at 1/4 & 3/4 positions.
I mislabeled the 4 sub graph... but one look and you'll be able to see the results of each sub and the result of all 4 subs after time alignment.
THD is under 2% at my normal listening level at 10Hz, under 1% above 11Hz, and under 0.5% above 20Hz when running sweeps at -15dB on the master volume.
I have no idea what THD is at reference level because my Umik-1 clips to the point it's not reliable by 14Hz on a sweep at 0dB master volume.
Of course there's room for further improvement, and I'm sure I could re-position subs even more, but I don't really think the juice is worth the squeeze considering where it's at now.