Frankly, I wouldn't consider the x200 at all. It only has a 6.5" driver, and even though it has a passive radiator that's simply not going to cut it. Not for HT, anyway.
You said your room is 16x17, but didn't mention the ceiling height. That's critical when deciding on a subwoofer, because it's the total cubic volume of space that comes into play. Just one foot difference -- say 8 feet vs 9 feet high -- makes a volume difference of about 12%. That's significant. How high are the ceilings?
In general, dual subs are better than a single one. That configuration is more capable of mitigating "room modes", which are a whole other topic. Suffice it to say, it's not something you want. That being said... when running duals you need to consider the quality of what you buy very carefully. Depending upon the circumstances (budget mostly), it might actually be better to get a single good sub than 2 mediocre ones.