So many choices.... should be easy though
I took the time to look at the speaker system you have. Look really nice and most all of the people who have them like them for sure. As I am sure you have seen there are a lot of choices, good choices, for you to pick from. I do not know what your budget for the sub is. However do not be afraid to spend some money and get a good quality sub. There are a tremendous amount of choices to be made up to the $500 mark. Not to say you have to spend that much, I am just stating that there is a tremendous selection to choose from up to that $ range.
Do not doubt the importance of this speaker in your system. It will bring another whole world of listening pleasure into your room. It will make movies come to life and will give you the nice warm bass when listening to music. And if you want, it will make things come off of your shelves if you want it to.
I have seen tremendous reviews of SVS, Rocket, Paradigm, Klipsch etc. and am sure that they all are great. GIving your room size you really do not want to get a massively powerfull sub, anything in the 150 375 watt range would be more than enough I would think. I have a Velodyne DLS-3750R and am simply blown away with it. Waaaaayyyyyy more than I expected and would play just fine with speakers larger than yours. If you ask me I say Velodyne from expierience. But you must take into consideration the vast knowledge of the great folks here on this site. They can lend differing opinions than I can. But I will guarantee you 2 things, 1) If you buy from a quality minded manufacturer with a good reputation, & 2) if it is connected and positioned properly you will not be able to keep the smile from crossing your face when you here it the first or 10,000th time.
Do your research, listen to the other great folks on here and you will be pleased indeed.
