Which subwoofer?

I have a small room (10’x14’) and am wondering if a subwoofer would help. If so, which one?

I have Martin Logan electrostatic speakers with  8” powered 200 watt woofers and 8” passive radiators.  The bass is articulate, but not very deep. I am wondering if I could get more bass volume and depth without loosing detail with an additional subwoofer?
I have tried an 8” Velodyne, but could never integrate it with the Martin Logans so I sold it. 

The Martin Logans are powered by a 200 watt McIntosh receiver. 
Any thoughts?

@bdp24 - thanks.
I know oldhvymec loves his OB too.

@oldhvymec - have your well fed chickens started laying Emu eggs yet? They are large and dark green, thought I'd share that, might save you puzzling over it in the future if they do :-)
I'm a huge fan of my SVS PB2000. I've owned Velodyne and Monitor Audio subs. This SVS is in another league. House shaking low end, great control and presence. I enjoy the ability to use the phone app to really dial it in. For me it would be a no-brainer. 
I've owned Velodyne, SVS and RBH subs - and now have a JL F112 V2.  The JL is in a completely different league in my system.
My main listening room is 13’x9’. I run three HSU subs. To my ears,they work very well. 
Martin Logan makes push/pull subs (top of their line) that are fast and just right for your Martin speakers. -1 For Hsu or ANY brand that have drivers that face downward, passives are okay, but not desired in my world. 2¢