Not sure what your budget is but electrostatic speakers usually equate to dips in impedance throughout a song. Look for amps that can go down to 2 ohms (or 1 ohm) and remain stable with no meaningful increase in distortion.
I'd suggest the new Bel Canto REF1000 II, Spectron MK2 and I'm sure there are others that can meet the 2 ohm spec.
I'd suggest the new Bel Canto REF1000 II, Spectron MK2 and I'm sure there are others that can meet the 2 ohm spec.