KLH model 9 electrostatic Speakers

@rdiiorio , you have been at it for a while! Most people back then though the SOTA was Marantz Model 9s driving K horns. If you were volume centric it was but if you cared about realism the KLH 9's were it. The only fly in the ointment is that the KLH 9's are not capable of realistic output and bass. It is hard to recreate the visceral side of music. ESLs do not project power well until they become full range line sources. The panels have to extend from floor to ceiling without gaps. Add subwoofers to such a speaker and what you get is the nuance of an ESL with the power and controlled directivity of a large horn. Currently only Sound Labs makes such a loudspeaker and it is darn impressive. 

"Will Dynaco st 70 watt good enough power for the nines?"

Depends on how loud you listen. I would love to hear the 9's with something like a Pass XA 60.8. Parasound JC 1+ would be overkill. 
I am not familiar with the Plinius amp but if it sound fine stick with it. It is a 100 watt/ch Class A amp which in my experience should be more than enough. If it sounds anything like my old Krell KMA 100's you should be in hog heaven.

Ralph, why not just put 200 watt 2 ohm resistors in series with the speaker. Yes, they would absorb some power but they would cost only $40 dollars and I bet you would still get 60 Watts out of the M60's. The other thing is the roll off would be way up there and I doubt most of us could hear it?

@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!

Right, there is little to no current drain for an ESL bias supply, just high voltage. Power cords make no difference. The bias supply can actually drift up to 10% and you probably would never hear it. I can decrease the power by 500 volts and you can not hear a thing. 

KLH 9's like Quads are very intimate speakers in spite of their size. They sound best close in and close together. The 9's are certainly more reliable. But they are touchy speakers to set up right as the high frequency balance evolves as you go off axis or change height. You set them to sound right at the listening position which is the best you can do.
Acoustats were the first ESLs that had reasonable dispersion and were truly indestructible. As they evolved into the 8 foot tall "plus" models things got really serious. Now you have full range line sources capable of projecting more sound into a room with much less distortion than any dynamic loudspeaker that was not itself a line source. Sound Labs further refined the ESL giving it a perfectly even dispersion pattern over 45 degrees and even more detailed imaging. 

Having used ESLs with occasional interludes with planar magnetic and ribbon speakers since 1978, I have return permanently to ESLs. IMHO nothing trumps a line source ESL. It is the loudspeaker with which you are most likely to achieve the absolute sound. As JGH said back in the 60's with the Model 9 you don't listen to the loudspeaker. You listen through it. I think that applies to all decent full range ESLs. I close my eyes and I don't hear loudspeakers any more., they disappear.