I will concur on the subwoofer that bandphan has suggested in comparison to the Klipsch, The MFW-15 is a large ported sub that will absolutely put the Klipsch with a larger amp to shame in both output, SQ, looks, and performance.
You have a large room which you will need a larger sub to pressurize, If you choose a smaller sub, it will run out of juice long before it has any impact on that large room. Then you will either spend more money to get another sub to add to the one you got, or you will have spent money on something that just doesn't cut the mustard and will be in search of another sub to replace it.
Just because you have a larger more powerful sub doesn't mean you will have to use it to its full potential, but at least you have it in case you want it, and it will not struggle like the 12" would be pushed to its limits and beyond.