Subwoofer

I also do not believe in running my main speakers through the sub's crossover just for purity's sake. I know there are certain advantages to doing so but I like to keep the mains as clean as possible. This way also allows you to just turn the sub off when not wanted or to compare with and without.

Ricred1, I hope you don’t mind me chiming in as I have enjoyed this thread and am considering adding a sub to my system.

I am driving a pair of Esoteric MG 10s in a room ~12.5 W x 15 D x 8.5 H. Though I am convinced that more than a single sub is best I would like to start with a single. I also think I would like to continue to use my 10s full range.  They drop off rapidly below ~50hz. I would be willing to buy a used sub to experiment with as I could resell it if desired. I believe a close box might be best, with variable phase. Any suggestions on a sub or my thinking?

I like Velodyne's DD series because of the room tuning and ability to play below 20hz.

Mesch,
I've owned Martin Logan Depth i, HSU, SVS Ultra and now the JL Audio F110s V2s. I have dual F110s with the CR-1
Crossover. I prefer the F110s over my previous subs. That being said, I'm selling my subs, crossover, and Aerial 7Ts to purchase Monitor Audio PL500. 

In a room your size Mesch, I think the DD Plus 12" would be good. Velodyne has a chart on their site. Adding another later will work great.