Golden ear sub x

Your 3.7's are a very fast and detailed speaker. You need to make sure you get the right sub or you will not be happy. Since your speakers are time and phase correct, I would keep it that way. The Vandersteen 2qw sub uses 1st order xovers. Its also very adjustable, and is meant to be used with the type of speaker you have.

" Columbia interconnects and type 4 wires "

The Columbia's exceptional, but the Type 4's are not. If you replace them with Type 6 or 8, you'll be glad you did.

The Velodyne is a fsr 12, never blended well with my 805 diamonds in my basement system either?I picked up a b&w cts w 12 passive sub,using a processor to xover and a Emo xpa 2 bridged to amplify awhile ago to go with my 805s  in the basement and I'm very happy with the result.Better bass then I ever had!Tried sub with my Thiels and it sounded very good,much better than the Velodyne ever sounded!Thats when I knew Velodyne had to go!The b&w is a sealed sub and weighs 60 pounds with no amp.The Vandersteen sub is an interesting idea!Music Direct sells them in Chicago by me.I agree that my speaker wire is not up to snuff yet also,just trying to upgrade as I go along.Thanks for all the responses!I really appreciate it!

The SVS SB13 Ultra is a good consideration. I have two and they work well. Very fast, although they probably don't have as much output below 20 Hz (movies) as the PB13 (ported box), which is significantly larger. Plus, SVS has a 60 day free trial (with paid return shipping), and an unlimited 5 year warranty. Good deals off of their outlet page as well.