As per your topic ...It takes upto 4K rms !
But do you see Soundstream XXX series 18" sub specs ?? Its rated at 10,000 watts rms baby 
Some Cautions from official site:-
When it comes to high power subwoofers, there's "good", "great", and then "simply badass!" The XXX subs are obviously in the latter category! The 15" is alone no more with the release of the XXX-18 earlier this year. With Quad-1.2 Ohm voice coils, the applications are endless and appropriate.The 120 pound wooden shipping crate is a nightmare to move, but when you and a friend heave out the 91 pound beast, nirvana will overwhelm you...
[I]Now, for a word from our attorneys: "Insane amounts of SPL are healthy! However, if you shred your flesh, crush your skull, launch your eyeballs or pulverize your brain, SOUNDSTREAM IS NOT LIABLE, PERIOD!!!" Be safe - use with caution...
Soundstream - XXX Subwoofer
i will later post videos of EXO and Justin Yokun who are true lovers of XXX series ,Both got Insane setups! [/I]