I agree with what has been posted. You need a big sub and big power. One thing that will help a lot is if you could do something near-field as in directly behind your seating position. Even a single sealed 18" will give you good tactile feel down to close to single digits. JTR S1 would do it nearfield, PSA s1801 would probably work too and be your cheapest/smallest option. But not everyone has the room for a big sub behind their MLP. You could try 1 of your 15" you have now to get an idea of what it is like if you have the room, fire the driver into the back of the seat.
But as for having subs out in the room and wanting to "feel" them at 14hz. It will take multiples of some very powerful subs. It probably won't happen with just 1 unless it is something along the lines of a JTR 2400ULF or 4000 ULF. You are going to need to spend $2000-3000+.
HTPC, Sony 40es, 120" Silver Ticket, 7702mkii, Sunfire Amp 225w, JBL 590, JBL 520
PSA XS30, Seaton Submersive, 2 Um-18 8cf sealed, Outlaw Ultra x 12, Kappa Pro 18LF, BFM Tuba 60 horn, B&C 18TBW100 6cf 41hz, 34hz, 28hz tune
iNuke 3000 & 6000 DSP's, Crowson Motion Actuator