If anything the holes are just damping the wrong frequencies or are more broadband, though sometimes when the damped phase of the modes interact they do non-intuitive things! If I recall the Auralex design it was a broadband version with different volumes for each hole? As a coke bottle changes blown frequency depending how much you drink - same principle.
Portholes work on the same principle a port in a speaker does - you ever hear what happens if you stuff a sock in a speaker port? The mass of air in the hole needs free to vibrate in the hole - otherwise it is not a Helmholtz. Pegboard is the same principle - smaller holes but more of them.
Maybe Dennis knows his own article citations - I would have to dig thru the mag stack....you could easily retro in the corner cutout register vent he was suggesting though unless it is in the walking path (your wife does not want to catch her heels in a vent!)
Doubling up subs on the front stage makes it worse not better - you would just be driving the modes even harder - to combat length modes you need to have a pair in back - if they were smaller they could fit in the back columns - but I think your walkway is in the corner so subs cannot go there if they are as you say big bastages The best analogy is a kids swingset - you get mom&dad pushing in the direction of the wave the kids goes faster and higher - but if one pushes the wrong way - the kids takes a spill (kills the modal wave)
Anyways I just checked my SubSpace calculator for an all corner sub placement often a great solution for keeping your SPL up whilst killing modes. The problem is you are in the null of the third length mode but at the peak of the 2nd/4th modes- you still get the dip in between them because they are so strong http://krasmuzik.biz/portfolio/Kellog_4corner.pdf
. You can mitigate that by moving back or forth off center and/or dropping them with a pEQ or killing the 2nd with quarter wall placement http://krasmuzik.biz/portfolio/Kellog_4quarter.pdf
and mitigating the 4th with lower crossover and placing your LCR'S in the null or near at 1/8 length.