Thanks for the details, I've got a better idea of what you're doing. I missed the post #9 somehow. "118 db+ at 10hz before EQ", I don't see that being a problem, but I'm not perfectly clear on all details,...it'll be fun to follow along.
With regards to PVG;
Pressure Vessel Gain (PVG) is the scenario whereby the longest dimension of the room can no longer support full propagation of the waveform. At this point, the acoustic propagation transitions to acoustic pressurization. The manner in which the sound is reproduced into the space changes from a normal cyclic propagation, to pressurization because the wavelengths are too big for the space.
The frequency at which this occurs is approximately the point whereby half the wavelength of a given frequency is equal to the rooms longest dimension. So if your room has a longest dimension of around 31 feet, the transition from propagation to pressurization will occur about 17-18hz. This is because a 18hz waveform is 62.7' (1130/18). Half of that is 31.39', so this corresponds to the approximate length of your room. As I stated, this is the point of transition. Any frequency below that point pressurizes the room, and any frequency above that point propagates freely. So in this room that's approximately 31 feet in the longest dimension, from 18hz downward, the room gives back acoustically.
At this frequency, the results are a gain in acoustic pressures in the room that grows as the frequency decreases. This acoustic support reciprocity, is theoretically 12db per octave. The percentage of the 12 db/octave gain one achieves, entirely depends on the integrity of the boundary walls and surfaces. If it was the theoretical concrete bunker, a full 12db/octave boost would occur. Typically, somewhere between 6-10 db octave could result. Also, in addition to the walls and surfaces flexing, other aspects may affect the point at which room gain begins. Furniture, cabinets etc, anything that consumes a certain measure of cubic feet, may slightly alter the transition frequency merely because the items take up space.
It certainly sounds like you're going to put some very nice gear in a very nice room. Good lookin' out.
Thanks for the details and good luck