I have Sound Lab ESLs--dipoles, like yours. I have tried a number of subs, but they always sounded like separate speakers. I have had a theory that OB dipole subs might sound better with the dipole ESLs. Maybe my theory is wrong, but my results aren't. I am using double GR Research SW12 16FR servos on each side of my ESLs. The H-Frames were easy to build; the price is right also, and include the amps necessary to drive them (built-in servo loop) I am thinking about getting 2 more pairs and stack them on top of the other ones, but I'm not sure I really need them. I listen almost entirely to classical music.
Chuck