You have a big room of 380 sqft and two sealed bass sources in you mains.
The problem with bass in home listening situations is that it is very modal in nature. What we hear is not only direct sound but direct sound and combination from multiple reflections. This gives rise to peaks and dips in bass. The bigger the room the lower in frequency the peaks and nulls are. This issue is of high significance in bass due to the fact that we dont have ability to differentiate between the direct and reflected sound in bass. What we hear is the combination. We hear bass in steady-state. The bass that one gets in listening position thus will be far from even what the alignment used suggests. Peaks and dips as high as 15dB are common in typical rooms. Rooms simulations dont help much either because the real room is very different due to windows, openings and furniture etc which hardly gets captured in simulation. Bass traps dont help much because the wavelengths concerned are large and lot of bass traps would be needed to really tame the reflections. Global EQ also does not work in the modal region
Bass in rooms is thus a spatial-steady state problem and needs a spatial-steady state solution. Much of what I am writing is from the below links which are good sources of recent work in this area
www.gedlee.com/downloads/OptimalBassPlaybackinSmallRooms.pptx
Good bass will need distributed bass sources. Even the mains can serve as bass sources if they go low enough and have shallow roll offs.
So, since you have mains that go low and have shallow roll offs, its a benefit that you can use. I would suggest an overlapping distributed bass solution, a 4th order bandpass subwoofer will perform very nice in 2 octave 45hz to 180hz bandwidth. The bandpass suppresses all higher order distortion harmonics and hence produces very clean sound. Below 40hz (ie below modal region) multiple subwoofers will combine in phase and so global EQ can be used to equalise the lowest octave.
Make stereo bandpass subwoofers and use just about any decent driver + amp. They are not really critical in the system. Some of the car subwoofers are infact very good. They are robust and have the right parameters like excursion and power handling. The amp can be a simple stereo amp that can go till 20hz and have sufficient power.
Use minidsp for crossover+EQ. One unit will suffice for a stereo sub.
Then take measurements to get a flatter response in the listening position. The resulting bass is tailored for the room and will be similar to the bass that we hear in headphones.
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