Subwoofer for 2 channel high resolution system

What sub is suitable for music. Would like something that would mate well with a system that is transparent portraying excellent sound staging and imaging.
Basically I am looking for a first rate sub for music. One that will disappear, but add the bottom that will take my system up a notch.
Also need balanced i/o, and a high pass to amplifier.
You will pay as much as a top flight preamp for these, but the Wilson Benesch infrasonic generators are the fastest, most true sounding bass units out there!

they feature they're own amps and have a slew of function capabilities

they can blend seamlessly with box, planar, electrosatic etc...
Larry Greenhill thought well of the SVS PB13-Ultra ($1600) in the last issue of Stereophile when mated to his Quads. If you set the level correctly, any sub will disappear.
I would go with either a REL or the Wilson Benesch.
The REL Studio would be a sure bet. Amazing how it transforms the whole soundscape! I also tried the Stentor and Stadium, but could not come close to the Studio.
I am enjoying a Rel B3 with my modest 2 channel system.

The B3 is purely a very low octave "augmentation" in my system.

Sorry, I do not know about high pass or balanced inputs. The Rel works so well in its recommended manner that I have no desire to try it any other way.

Room placement made considerable and easily audible differences, in both quantity and most importantly quality.
I would go for either a Rel Studio or Stentor. A Stadium(no longer made) may work also, depending on you're system and room size.
Which sub's are of higher caliber? Wilson Benesch, JL fathom, REL, Velodyne, Revel, Kharma, Martin Logan, Paradigm, Sonus Faber, NHT, Wilson Audio, JBL, HSU, B&W, JM Labs, Tyler Acoustics, Von Schweikert, Avantgarde.
Which ones are the fastest and natural sounding?
From what the mags have been saying the JL Fathom's seem to be the ones- do audiogoners agree? If so what else is in that league?
Which ones are the fastest and natural sounding?
More a function of the room and setup than the sub itself.

Spend some time looking at the independent subwoofer tests:

And this ranking is interesting:
Bob is right. You need to test drive some of the subs you listed. I tried Velodyne and B&W before a ended up with a Rel. The Rel just blended with my room/system better(even though I run B&W speakers). Good luck!