Oh come on man, we were
this close to making something like the first ported IB that I know of
It would have shown that it can be done, and the benefits are real. Maybe just wall it off so that it looks like a small equipment room? That would protect the drivers from everything.
5.5 x Sd? I'm not sure what you mean, I'm referring to the height, width, and depth of that section right behind the drivers - not the large open space, just that wooden area that has the louvered pannel.
I'm not saying your room can't give gain, it just doesn't look like it is for the location of the IB measured at your seat.
Non spec IB15s with a 35hz Fs....hmm, that's no good. Whether you still have any interest in the ported IB or not, I'd take the crossover and BFD out of the chain and do a close mic sweep and one at the seat, that will clear some things up. I would highly recommend you reconsider this ported IB idea one more time though
You could be the first of many.