high end subwoofer...which one tho?

That's a small room for now and you would not 'need' the formentioned however it would be useful and work later for a larger room. I would opt for a svs 13...just because of the fact why pay more. Take a look at Elemental Designs (ED) subs as well. Killer performance, killer price, and free shpng for something that weights as much as all your gear put together.

The SuperNova MKIV-12 is terribly insane in performance, with more than 100 decibels of power...it will shake the walls.

I have 2 definitive technology supercube reference subs in a 14 x 22 foot room. These have one 14 inch sub with two 14 in radiators. Internal amp 1800 watts. They are awesome for two channel and HT. cost $1900 each.

I own 3 Velodye Subwoofers, and I could not be more pleased.
Never ANY issues with any of them, they integrate very well.

Maybe not the $$$$$ The most expenxive but, IMHO with the right power cord,
and interconnects, proper placement, they are VERY hard
to beat.

At 12hz. I don't feel like I am missing anything.

Fast, tight, DEEP, extended Bass, with little or Zero Distortion, unlike other "huffers".

Both music, and movies, are played with tremendous
clarity, and dynamics.

I use a 1 18" and 2 15" and once calibrated for the room,
it is true, multiple subs. do "smooth" out the bass,

It's NOT about more Bass! But, cleaner, tighter, faster,

Bass!

It is the same as implementing mono-blocks, multiple

sub-woofers take the load off the single unit; Allowing
it to play without ANY strain, cleanly and deeply as
they are intended to play.

I LOVE MY MUSIC!

I vote for Aerial SW12 or Audio Physic Rhea 2. The Aerial is most powerful, but the AP Rhea2 a bit more tight and dynamic. Above these you have the Burmester S8. It costs a lot, but it is the best sub I know about for music.

JL Audio is also good (almost as good as the above), but be awere of that they lack speaker level input. That´s why I won´t reommend them. When it comes to music it is always best to connect subwoofers to amplifiers using speaker cables instead of interconnects from preamp.
I wouldn´t care about the Velodyne unless you really need the room correction functionality.