Looks like a text-book example of the Allison effect.
Inspecting the graphs, the dips in the region between 100 to 200 Hz indicate that the room boundaries are approximately 1.5 to to 2.5 feet from the woofers. Even if you move the speakers farther away from the walls, the floor bounce will remain because of the height of the speaker stands. This is why Allison speakers. had woofers near the floor.
I would suggest getting two woofers or subwoofers one for each channel, NOT mono, preferably corner placed and use a high crossover frequency around 200 Hz to the satellites. SVS and HSU woofers would likely workup to this frequently . You will need some type of DSP to do the crossovers, set time delays and DRC.
Off the top of my head, I can’t think of an alternative solution. Other than redoing the room or using massive amount of treatment..
Edit: FYI - To first order, for one boundary, Wavelength of null = 4 *d (approx) where d is distance to boundary. Frequency of null = speed of sound/wavelength