I've no personal experience with two subs, but this is what I've read elsewhere about it.
Having two subs will not provide a lower frequency response than either sub is capable of. However, two subs can work in your favor in one of two ways. If you co-locate them (stack them one on top of another) you can gain an increase in headroom (play louder without negative consequences, such as distortion or bottoming the driver) by 6 dB, I think. Or is it 3 dB? Another senior moment. Regardless, you can play your subs louder than if you only had one.
If you chose to place each in a different area of the room, you don't gain anything in volume, but you can improve the overall smoothness of bass response throughout your room (i.e. achieve the smoothest bass response over a larger area of your room). If you go with 350s, two of them would definitely be helpful
On the other hand, the 500 and 600 use DSP technology to provide a surprisingly smoother frequency response than your average sub. The 350s don't use this technology.
So, assuming I know what I'm talking about (hmmm?
), it comes down to two 350s for either louder or smoother bass, or one EP500 or EP600 for lower bass with smoother frquency than can be achieved by one 350. It all depends on what you want.
I have no doubts that a 600 could fill your room (4410 cu. ft.) with plenty of low loud bass, and I suspect that even a 500 would please you. I have my 500 in a space a little more than half the size of yours (1656 cu. ft., plus a dining area of 800 cu. ft., plus a small foyer, for a total of around 2500 cu. ft.), and it certainly gives me all I need.
The best suggestion I can give you is to give Axiom a call, describe your room (size, openings, furnishings, etc.) and see what they would recommend. They will surely know more about this than I do. You'll find them friendly, easy to talk with, and they will not try to hype you into something you don't need or want. They are more interested in having a satisfied customer than in making a quick sale. It would be well worth the cost of the phone call.
