Yup... I forgot to convert my inches to feet...
I can go up to 92"... but even at 12" x 16" x 92"... that's only about 10.5 cubic feet or 297 liters.
I guess doing a pair of these is not gonna be feasible, unless I make a weird shaped box ... like maybe an L shape with the 12" x 16" x 92" on the bottom opening up into a 24" high x 8" deep x 92" wide/long section on top of the bottom section. That would still give my recliners plenty enough room to function properly and would make the total unit somewhere around 40" tall including the downfiring section.
It really sounds like I probably need to just try one sub and maybe go with EP1500 which should be a lot more power into the one sub... it's rated at 800 watts bridged mono into 8ohms. It's showing 1400 watts into 4ohm bridged mono but that is only at 1KHz... so I don't know the real power rating, but it makes sense it would be at least 800 watts.