The ESL57 drops to around 1 ohm at HF. Driven with a stable solid state amp with low output impedance this isn't a problem. The issue arises when you try to drive them with a tube amp where the output impedance is usually higher. In this situation the power transfer function worsens with rising frequency, hence the often heard roll-off.
That was why I designed these GM70 monoblocks, to drive some large electrostatics. The problem I find with SS driving statics is unless the amp has a very refined top end the panels will reveal the hardness in the top.

Nelson Pass F4's do a very good job of driving statics as well.