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?