Just to elaborate a bit more...
Subs only cover about 2 octaves, from 20Hz to 80Hz. In that range, the room has so much influence on performance that you can't think of the sub as a speaker, you have to think of the sub and the room as the mechanism that produces sound. This is more true of subs than any other speaker type. For your mains, yes there are room effects, but they are mostly reflections that can be dealt with, and response issues that can be equalized out. But for a sub in a room, what you hear is actually the excitation of room modes, standing waves if you will. You can't have sub bass without them. When modes add, you have emphasis at that frequency that you can equalize down, but when they result in a response null, you also can't eq response back up. Changing the room dimensions or shape totally changes the entire picture, and where you place the sub determines which modes get excited. You can't ignore the room, and just focus on which sub to get. Even a fantastic sub in a bad room or bad location won't sound good. We can argue if a good sub sounds better in a bad situation or not, but that's really ignoring the entire mechanism, sub and room together. It also serves little purpose to concentrate on sub design, maximum SPL or minimum frequency of a sub alone. There is so much more to it than that.
As writers of opinions here, we can't see your room, can't measure its response or hunt down ringing modes, can't play with sub position, bass traps, or anything. All we can do is talk about subs and their merits, again, half the picture.
What I've been trying to say here is that when you use multiple subs you increase the chances of exciting more room modes, which in turn results in smoother response, and the impression of better bass. As a contrast, consider subs in the car stereo world, where the work at one note..about 40Hz. They rumble down the street making tons of 40Hz. But they couldn't do 30Hz well, much less 20Hz. It may be impressive to be loud at 40Hz, but it's not a good solution for serious low frequency reproduction. Modes in a room may not be that bad, of course, but the point is similar.
When you use more subs in an unknown room, or a difficult one, you statistically increase the chances of even response by exciting more modes. That's actually far more of a positive contribution to the overall performance of the system than having a single high performance sub that can't get the room working with it.
That about does it for me, I know others may disagree.
If you want to get something you can try and send back if you don't like it, have a look here:
Perhaps there are better performing subs, even cheaper, but you don't have to commit to anything with these, send 'em back for free if you don't like them. In the trial period, you can move them around the room and experience first hand how important location is, how interactive the room is, and learn it all without investing permanently. Of course, you could buy something used and re-sell it if you don't like it. Not quite as good a deal, but non-committal.
Hope this all helps, rather that increases confusion.