01-13-15: GeorgelofiIn fairness it should be pointed out that there are many audiophiles and designers who would disagree with these statements, on both theoretical and empirical grounds. The relatively high output impedance/low damping factor of most tube amps, especially those using little or no global feedback, and the inability of such amps to double power into halved load impedances, will in combination with the impedance vs. frequency characteristics of the Ethos and most other electrostatics certainly result in less emphasis of the upper octaves compared to the presentation that would result with most solid state amps. However which of those presentations is more true to the source material, and which of those presentations is more subjectively preferable, and which of those presentations is less likely to trigger Jim's (Broadstone's) specific hearing issues, are separate questions.
But from what was said to get the very best from the ML Ethos you need an amp that can that can deliver good current down to at least 2ohms, so it stays flat over the frequency range, and not start behaving like a tone control at different load impedances.
That means "close" to doubling the 8ohm spec wattage to 4ohms and again doubling to 2ohms
01-14-15: Georgelofi
The Peachtree 220 from what I found can almost double into 4ohm giving 400watt but I can find nothing into 2ohm. If it gave 600 or 700 into 2ohm then this is the sort of amp that would not whimp out into the 1ohm of the the Ethos. And at 72 years old you don't want an amp that is going to curtail the upper mid/highs, because it's here where the Ethos are that heavy load of 2 to 1ohm, that will make a whimpy amp sound soft and dull.
And while it is true that when working into an electrostatic such as the Ethos the use of a tube amp, especially one which uses minimal or no global feedback, is likely to result in voltage vs. frequency characteristics at the input terminals of the speaker that are less flat than would result from the use of most solid state amps, it by no means necessarily follows that the frequency response characteristics of the acoustic output of the speaker will be flatter in the latter case. As can be seen in the comments by Ralph (Atmasphere).
Also, regarding the amp's ability to deliver adequate current into low impedances, it should be kept in mind that most music contains far less energy in the treble region than at lower frequencies, especially in the upper part of the treble region where the speaker impedance becomes really low in the case of the Ethos and many other electrostatics.
Regards,
-- Al