Personally, I'd go for a pair of subs - but a pair of 13 Ultras might be overkill for your room. I'd discuss it with SVS - and I wouldn't be surprised if they suggested that you step down to a pair of 12+. Either way, that's a pair of high performance subs that you're looking at.
I personally use a pair of 12" Rythmik subs in a similarly sized room (95+% music) and they do a tremendous job. On the rare occasions that video is employed and the lowest frequencies are present (effects) their performance has been beyond reproach.
I suspect that you'd be very happy with either of the SVS choices, the Rythmiks, a pair of 12" JLs, or a pair of the higher end 12" Hsu subs. All have credentials - be it a personal audition or a recommendation from trusted friends/contacts in addition to excellent test bench performance.
Good luck on the hunt - but I think you'll have a hard time going too far wrong.
Marty