Advice for Sub to match with Martin Logan Monolith III


Looking to add a sub to my Monolith III's,  like to keep it around $1,500 new or used.

Thanks,

Steve
stevepa
Yeah, me too. Like I said, I'm 95% two channel music. Maybe having a pair of nice subs will allow me to consider horns or panel speakers next as well. 
A lot of panel speaker owners use Vandersteen 2Wq subs.  New list is around your price range, although I bought two of them used a few years back for under $800 each here on Audiogon.  I don't have panel speakers, but I love these Vandy subs.  A great value IMHO.