I'll just add that using 2 subs can sometimes help even things out, but it can also sometimes make things worse, because you can actually end up with cancellations, in which case you would end up with less bass overall, not more. If you're going to use 2 subs, placement is pretty crucial, and if placement options are limited due to aesthetics, WAF, or space, you might have some trouble getting optimal results.
Personally I prefer to deal with room peaks and nulls by using a parametric EQ, I use a BFD with my sub to get a flat in-room response that sounds really great.
