It is not imperative the subs are identical. It does make it easier to set levels between them when the dials on each are "weighted" the same. Ie. 1 o'clock on each subs gain equalls the same output when they are matching.
Your room is definitely a tough one. Times ten. I'm guessing you can play your system very loud but the result never seems very dynamic. Is this the case? The problem is all of the openings and kitchen/dining area are sharing the acoustic energy intended for your viewing area. You are thinking duh.
. The sub is currently energizing your foyer with equal energy.
The cure is also the killer in your case. Another sub will give you a more dynamic experience without question. The downside is 2 subs in your main living space will energize the structure with ease on loud passages. All the sound energy must decay somewhere. Somewhere is everywhere in your case. This will result in modal peaks in locations outside your theater space. It can't be avoided.
Pound for pound, a sub is the greatest contributor to the dynamic experience in a home theater setup. I would argue even more for larger rooms. All higher frequencies are bolstered by a solid low frequency foundation.
Once you go 2 subs you wont go back........
