(Very, very nice intro write up. Very impressive)
5. Listening habits. for me...THIS IS SPARTA..for the wife...dowton abbey.
Could be trouble in Paradise.
And you also wrote fail all over the subwoofer project by limiting yourself in budget and restricting the size of the subwoofer cabinets.
A simple way of looking at it, one doesn't tell the subwoofers what to do as the subwoofers tell the owner what they want and if they're to perform at peak capability, they'll get their way. That sort of thing.
A room has acoustics and how the room's acoustics interact with the sound waves produced by the sub dictate the subs location, the owner of the room and the subwoofers are relegated to the authoritative position of head subwoofer mover as room measurements show the owner where the best location of the subs is to be.
Think of subwoofers like a cat or a wife, it's not healthy to a man's mental health to tell either, what to do.
In a room that size, my recommendation would be to get room measuring capability and four subwoofers, a few cases of beer and take some time to get these to all mesh together.
Since it's a basement room, three or four PSA, XS15's
would work very nicely. If the budget isn't there, buy two and add a third later. If the budget is still restricted, buy three Klipsch, RW-12d's from Newegg with an eye on a fourth. A suggestion, give up on the idea of stuffing these subwoofers into these cabinets as doing so limits one subwoofer choices, locks the subs into one location and you won't be able to try additional location as in the end, with measuring software showing you the acoustical way, you'll end up buying two, three or four more subs to make up for the deficiencies created by trying to herd cats made out of subwoofers into these two cabinet locations.
Just saying. And I hope the brevity of my above is found insightfully helpful as my above is not intended to be discouraging.