I too have CLS. I have a pair of home-built subs, using NHT1259 drivers in approx 2.8 cu. ft. enclosures. 2 is definitely better than one. If you have the time, inclination and skills, it's not hard to build better-quality subs than what you can buy commercially for anywhere near the same $. These two subs cost probably less than $600 for materials. Sure, you need an amp and crossover, but those are items you may have already (I did), and having them separate gives you more flexibility for future upgrades. I am more than happy with the way they worked out in my system, though I've been considering the Stryke HE-15 sub(s) as a possible upgrade/replacement. (www.stryke.com). Not like I need to replace these, but the Stryke driver just looks soooooooo nice.... ;-)
have fun,
-Ed Sawyer