@jayctoy , ESL have always been amp sensitive (not power cord senstive) They are also a very reactive load and their impedance drops dramatically as the frequency goes up. By 20K they can be under 1 ohm.
This has destroyed many amps. Current demands increase with frequency. Many amps will overheat because of this.
Back when JGH was reviewing the KLH 9's there were very few if ant high powered amps. Amps like the Crown 150 and Phase Linear 700 would overheat and self destruct. The best amps to use back then were the Marantz Model 9's and several Mcintosh amps. Today You would use a High power Class A amp with a lot of heat sink or an Atma-Sphere amp.
M60's would be perfect!