Best subwoofer for 2 channel Hi End system

I use a Velodyne HGS-15 with a pair of bi-wired KEF 104/2s. A Proceed processor sends everything below 80 Hz to the sub, which results in even more open and transparent sound, even though the KEFs are capable down into the 20 Hz range. Freeing stereo speakers of low frequency duty seems beneficial. (I use a Proceed Amp-3, and each channel can deliver 250 watts into the 4 ohm load of the efficient KEFs.) The KEF to Velodyne transition is seamless. I plan to add another HGS-15 on general principle, even though LFE is smooth and strong throughout room with a single HGS-15.

Aerial sw 12 hands down

1) Aerial SW 12
2) Revel B15
3) ML Descent
4) The other stuff
I listened to everything, and wanted the Aerial, but found the $1.5k premium over the Revel to be too much. So I ended up with two B15's.
If you think two is too much, then you don't know about bass nodes, or have a perfect room with lots of acoustical treatments.
Main speakers - ML SL-3's.

amp they use now. Very musical and an extremely powerful capability. No servo's needed here as distortion is quite low already. At 140 lbs quite heavy. VMPS has been getting great reviews on their bass since the eighties. Bass is typically articulate with natural weight but could be used for home theater too. For the money they are one of THE bargains in subs. One of the best benefits though is the advantage of being able to adjust bass "Q" to your room.

I would suggest the green mountain audio hammer. Better yet, two green mountain audio hammers.