A major problem with trying to reproduce bass in small rooms is this: The reflected bass energy bouncing off the room surfaces re-combines with the direct output to produce significant peaks and dips at the listening position.
For instance, let's assume you have a single subwoofer positioned along the front wall, between your speakers. There is one path length from the subwoofer to the listening position, and there is another path length from the subwoofer to the wall behind you, then reflecting back to the listening position. At the frequency where the difference in these two path lengths is equal to one-half wavelength, the bass energy reflecting off the back wall will arrive out-of-phase with the direct sound and a cancellation notch will occur. At the frequency where the path length difference is equal to one wavelength, the bass energy reflecting off the back wall will arrive in-phase with the direct sound and a reinforcement peak will occur. Similar path-length-related peaks and dips will occur based on reflections off of the other room surfaces.
The peaks and dips can be addressed with equalization, but I think there's a better solution. The problem is fundamentally an acoustic one, so let's analyze it that way and look for an acoustic solution.
Note the problem is not that there are too many of these path-length-induced peaks and dips in the bass region - the problem is that there are TOO FEW of them! They end up being spaced far enough apart to be quite audible. At higher frequencies we also have path-length-related peaks and dips, but they are spaced so close together that they combine into a much smoother reverberant soundfield.
If we were trying to be technical, we might say that in a small room the bass energy is well "correlated". What we want is "de-correlated" bass energy - that is, we don't want distinct peaks and dips resulting from reinforcement and cancellation. Fortunately, there's a way to de-correlate the bass energy in small rooms: Use multiple low frequency sources scattered around the room.
Going back to our original example, suppose we scoot the first subwoofer over towards the right front corner. And suppose we add a second subwoofer along the left side wall, slightly behind our listening position (but still not too close to the left rear corner). And we feed both subwoofers the same signal. Now the path-length-difference induced peaks and dips from these two scattered low frequency sources will never coincide anywhere in the room! So we have taken a major step towards smoothing out the bass everywhere in the room by de-correlating the low frequency soundfield. In my opinion this acoustic solution is superior to equalization using a single subwoofer because it's effective throughout the room, not just in one area.
So if the choice is between one big and two small subs, my vote is for two small subs scattered, and driven by the same (mono) signal.
Duke
