Nothing about a subwoofer has to match in terms of brand, so anything will pair well. Low frequencies aren't subject to a particular sound profile in the way a loudspeaker is.
So it comes down to how low do you want to go for movies and how big and ugly of a box can be tolerated. If you want seat shaking bass to blow your mind, it's a bigger budget and space, placement gets fussy with any one sub in a big room, particularly if it's open to other space.
I'm partial to SVS offerings for myriad reasons. Free shipping both ways with a 45 day trial period, full purchase price credit toward an upgrade within the first year of ownership. Wide range of performance and price. Subwoofer outlet for "scratch & dent" products which come in $50 to $200 cheaper and carry 100% of a new product.
For that size room I'd look at a PB2000, which runs $729 for outlet, $799 new. At a minimum, PB1000. Don't care for bone-rattling, look at SB2000 for $699 new, or the smallest SB1000 for as little as $450 in the Outlet or $499 new. Amazon and New Egg have the discontinued SB12-NSD for $400, and it's performance puts it squarely between the SB1000 and SB2000. No buyer return/upgrade benefits though.
Fair warning, some of those subs can be huge. Write down the dimensions and go find a box that size to better imagine it in your room. You don't want to arrive home to find a behemoth on your doorstep you didn't expect. Instead, you want to plug in the behemoth and be shocked by what come out of it.
