I've had good results with the Bugtussel Tegmentum sub (which I sell). The transmission-line Tegmentum has low coloration with good transient response (very low overhang), as well as an extremely flexible crossover/equalizer built in, which is especially helpful in getting a good blend with electrostats.
You might be able to purchase a pair of Eros bass cabinets from InnerSound. Once again they're transmission lines, for low coloration and good transient response. As I guess you can see, I think that transmission lines are an especially good match with dipoles.
Gradient makes a dipole sub which would probably be an even better match, but almost certainly doesn't go as deep as the big Tegmentum does.
Best of luck in your quest,
Duke
You might be able to purchase a pair of Eros bass cabinets from InnerSound. Once again they're transmission lines, for low coloration and good transient response. As I guess you can see, I think that transmission lines are an especially good match with dipoles.
Gradient makes a dipole sub which would probably be an even better match, but almost certainly doesn't go as deep as the big Tegmentum does.
Best of luck in your quest,
Duke