Bass management with stand alone preamps

^^ I don't see the B1 listed there either... Dr West is the designer of the Sound Lab loudspeakers.

No, I meant with the sub woofer. I know Dr West. One of my heroes. He has kept the faith and the flame alive.
Making an ESL sub woofer that you could use in an average room is a tough one. My own feeling is that ESLs having to be dipoles have never been good at deep bass and forcing them to do it just ruins the beauty of what they do everywhere else. Any dipole in an enclosed space is going to have the same problems but ESLs do not cross over to other drivers
making it worse for them. I would not ever use a full range ESL without a  sub woofer system unless you just listen to string quartets.

What are ESL? Martin Logan speakers?

Electrostatic loudspeakers. Martin Logans are ESLs from about 250 Hz up most of their speakers cross over to standard woofers. I think they still make one full range ESL. ESLs run on a different principle than regular dynamic divers. In the middle of the speaker is a charged mylar diaphragm. Charges up to 4-5  thousand volts are not unusual. On either side of the diaphragm is a "stator." This is a wire or metallic grid that is driven push pull by the amplifier through a step up transformer converting current to voltage. Like charges repel opposite charges attract. Thus the diaphragm is moved back and forth to the music. An entire 8 foot by 2 foot diaphragm weighs less than the voice coil of a 10 inch woofer. Every molecule on the diaphragm is driven and controlled 
by the amplifier. There is no cone flopping around.  The only disadvantage is that by design they are much larger than regular dynamic speakers. I believe their size is an advantage especially when they stretch from floor to ceiling producing a perfect linear array at all frequencies. They are typically dipoles ( they produce sound 180 degrees out of phase from both sides front and back.) Which makes low bass difficult but a linear array dipole is the best way to deal with room acoustics because of their radiation characteristics. There is no dynamic loudspeaker that can better the performance of a linear array ESL especially when they are mated to an appropriately designed sub woofer system. It is not IMHO either. Anyone who hears such a system is dumb founded. Anything from a single Block Flute to the Pixies is produced with a dynamic realism that I have not heard produced any other way.
Google soundlabs speakers. These are the best ESLs you can buy at this time. 

No, I meant with the sub woofer.

Yes- Sound Lab used to make the B1 subwoofer, which was a large electrostatic panel. 

These are the best ESLs you can buy at this time.

Agreed. IMO they are also one of the top five speakers made anywhere.