I have been debating with myself whether to let my post recommending dual Cap 2400's just stand as it is, or to come back to the subject. Desertdome's graph of the three options being considered on this thread, helps to put things in perspective. It is hard to imagine someone wanting to have more than 125db above about 30 or 35Hz, but fairly easy to imagine someone wanting to have more than 110db at ~15Hz, or more than 105db at ~12Hz. And, the Cap 2400's are going to have big advantages over the S2's starting at about 20Hz.
Of course, room gain can be expected to help make up for a lot of the difference in available SPL between the two subs. But, room gain can be somewhat unpredictable, so my personal inclination is to reach for the native SPL I want, irrespective of room gain. But, I'm not sure that I'm right about that. ScottieBN had also asked for advice on the PSA thread and I just caught up on the posts from the last couple of days. I thought that everyone was trying to be very objective and helpful. Sealed sub owners tended to recommend the S3001 or the S3601, and ported sub owners tended to recommend the V3601. Some posters tried to base their advice mainly on his room size, but I continue to believe that our own bass and TR preferences are just as important as room size.
The thing is that this JTR subwoofer thread has tended to attract slightly more extreme bassheads
, since Can created it. So, there is a somewhat self-selecting quality to the people who post regularly on this thread. And, dual Cap 2400's are sort of extreme basshead subs, in my opinion. The reality is that in a room that size, and on a wooden floor, at least 95% of the people on AVS would probably be delighted with dual S3001's. And dual S2's would be a nice step up even from dual S3601's. But, what about the other small percentage who really want to be rocked by their bass in movies? For them, ported subs can offer a lot more SPL and tactile response in that critical <30Hz range, almost irrespective of room gain. And, the tactile response of a ported sub is actually not influenced by room gain, so that has to be native to the sub itself.
Where I am going with this is that even if the OP wanted to buy ported subs, dual Cap 1400's would probably be more than enough in that room, much less three Cap 1400's. But, it seems to me, that if someone can afford to go with dual Cap 2400's, the additional low frequency SPL is still worth having. And, then he can still choose to have more or less low bass, via the use of the Low Frequency Adjust feature, depending on mood or specific circumstances. Any of the subs that ScottieBN has been comparing would probably work very well, but the Cap 2400's are for someone who really considers himself a basshead and who wants to remove all doubt about available headroom or low frequency SPL. So, it seems to me, that aspect of the buying decision is as self-selecting as participation in this thread.