Power increases into lower impedances!@roberjerman
One thing about ESLs is their impedance curve is not also a map of its efficiency, like it is for most box speakers.
Instead, its impedance curve is a result of being largely a capacitor. For this reason, what is desired is the ability to put out constant power over the range of impedances presented by the speaker rather than constant voltage (which results in increased power into lower impedances per the quote above). Of course, no amplifier really does make constant power but they can come pretty close, especially if assisted by a set of ZEROs (www.zeroimpedance.com) since any tube amp that is designed to make constant power (like ours are) will tend to have a higher output impedance.
For more on this topic, seehttp://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php