One woofer or a pair?

In my experience, the only way to get away with a mono sub is if the crossover point is exceedingly low, meaning less than 40Hz. Anything above that and you will be able to localize it. I also agree about the virtues of downloading; it seems to couple to the room better, but again will only work well with very low crossover points.

I agree with Kevin. During the x-mas season my REVEL Sub15 had to go from the right side to the left of the room (because its space was needed for the tree :-) ). Just this move changed my systems sound in a frightening way and I was happy when the season was over - at least in this respect.
It seems to me that it is a matter of your room how you think and act about subs in general.
Good luck!

From all above posts I think that if you're using a pair of woofers you can use them as a "sub-speaker" and give it to work with higher freequencies than 50Hz maybe even upto 200Hz.