Best Subwoofer To Use With A Two Way Speaker System

I received my new Wilson-Benesch Vertex stand mounted loudspeakers in mid-January.  After about a 200 hour break-in period and a few position tweaks I am now in audio nirvana but without the final low octave or so.  I carefully chose my associated electronics and couldn't be more pleased.  My Sutherland N1 preamplifier has 2 outputs so I can use it to drive a crossover/subwoofer system.  
I am entirely certain that my spouse would never stand for me to add a W-B Torus Infrasonic Generator & the accompanying Torus Amplifier at about $12,000. I would like some assistance from those that have the experience to advise me of something very good to mate with my system at a much more reasonable cost.  Thanks

To "m-db"
Regarding the Sutherland N1 Preamplifier that I selected for my 2 channel system.  Prior system configuration was using a home theater setup with initially a Marantz 7701 Pre-Pro and later a Marantz 8003 Pre-Pro with a Sutherland Ph3D Phono Stage.  Not really ideal.  Next came a long distance move and my decision to go back to my "roots" so to speak and configure a new 2 channel system.
My long term friend/engineer/dealer & turntable designer George Merrill and I discussed preamplifiers.  He and Ron Sutherland have had a long relationship and collaborated on some engineering projects.  George uses Ron's N1 exclusively and Ron uses George's Merrill-Williams 101.2 Turntable exclusively.  Probably the 2 most under-rated components.  Neither actively pursues reviews so what exists is strictly gratis from the industry. George installed the Ortofon tonearm and cartridge on my VPI.
In George's opinion there is nothing better than the N1, only others that cost more and never really deliver anything that matches it.  Ron combines his finest phono stage and his excellent line stage in complete dual mono perfection.  It provides 2 outputs, 6 inputs with the last being a white noise generator for component/speaker break-in. It can drive reasonably long interconnects without problems if the interconnects are not unusual in resistance or capacitance.
The sound of the phono stage lacks any coloration. If you find a review of the N1 the reviewer's only comparison is with whatever else they are familiar with and draws conclusions from that bias. This is of course a single-ended device. Ron wouldn't have it any other way.  Less is more. Fewer parts and a shorter signal path.  I did a home audition of an Ayre Preamplifier. No slouch in it's own right but the N1 was clearly superior to me. It simply allows your cartridge to present itself without the preamplifier getting in the way. A lofty and rarely realized accomplishment.  Even though there are a lot of preamplifiers on the market, from my experience there are not many great sounding preamplifiers to choose from.  Add in the distinction of being a full-featured preamplifier and the list grows very small very rapidly.  Loosing a separate phono-stage is huge. It eliminates more interconnects and the potential for noise. Yes the N1 is quiet.
In the end it was a no-brainer as all my components are single-ended. I own a vintage Precision Fidelity C-4 Dual Cascode Preamplifier that had to have the power supply rebuilt and now that it is back I am having fun listening to it's line stage which is really really nice. The phono stage/line-stage just can't create the details/micro details/dynamics & micro dynamics of the N1.
My previous loudspeakers were the Dayton Wright XG 10 Mk II Electrostatics' and the B&W 804's.
Link to the N1 owners manual:
Link to George Merrill:
It is truly wonderful never to look back in regret when you know you made the right choice!
Best regards,

Ahem, cough, cough, didn't I recommend the Vandies first?
No problemo, I am glad you are considering them. Unless you have some weird amp, they are sub that seamlessly integrates with you speakers.

Gee whiz! ANOTHER sub that integrates seamlessly? I've never had a "seam" problem with my B&W.
You absolutely did and I apologize for the oversight.  You get first creds!
Thank you