Actually considering port difficulties, and the 12.5 cubic feet you have, I'd be considering 2 woofers on each out-of-sight side, kind of slot loaded into the corner and loading each other. Well stuffed, Q low, would probably extend really well with room gain. Higher driver cost though, unless you used somewhat less godly drivers.
P.S. We DEMAND a build thread, we wanna see this!
Been thinking about this and grabbing 2 ultimaxs while on sale. Have a few questions on how it would work.
1 are you talking sealed?
2 Would it be two box’s in “one” or Would they just share the space inside?
3 How much output would gained