subwoofer mate for reference 3a de capo's ?

I'm trying to find a subwoofer which would be a good mate for a pair of reference 3a mm de capo i's
My system is similar, Sonus Faber Extremas or Electa Amator 1's paired with 2 sunfire architectual signature subs. What I really like is the fact that these are single driver units, it makes room placement less of a pain. No midrange smearing with these, dimentions are great too 13x13x13. Previously I had a pair of velodyne f-1500r. The carver is far superior...Hope this helps Scot
I'd check out the new Velodyne DD series. Try the DD-12 or DD-15, nothing else comes close. There's a reason for all the rave reviews.
Get a HSU , if you set it up right you will never know it's there.
The Alon(now Nola) thunderolt subwoofer is excellent