Just to throw in a few facts here.....
1)
The designs for electrostatic speaker amplifiers being discussed here (the ones fro TAA) were published in the 1970's and thereabouts. This was in the early days of the Internet... They did in fact turn up on the Internet after that, and I've seen occasional copies of them. They're difficult to find now simply because they are very old, and so weren't widely distributed - and not on sites that are still around, and nobody looks for them very much any more. At one point, TAA offered all of their back issues in electronic form, on CD. if you do a bit of digging with various search engines you will still find many of them.
2)
I should also point out one of the main reasons why DIY audio equipment was often overbuilt in those days. It's very simple, but not necessarily obvious if you weren't around back then. In the early 1950's through even the 1980's, there was a lot of high quality military equipment, and a lot of mil-spec parts, available as military surplus at absurdly low prices. A part that cost hundreds of dollars on the retail market might cost $1 surplus... and the military had a well-deserved reputation for using ridiculously overspecified and expensive parts. For example, test equipment was often rated to operate at temperatures like -50 degrees (just in case you needed to run it in the Arctic). Therefore, it became common practice among DIYers to use parts like Pyranol capacitors. A 20 uF/600V Pyranol capacitor was about the size of a can of Spam, weighed over a pound, had excellent electrical properties for many applications, and cost a lot... and, yes, they lasted forever and were virtually indestructible. However, you could pick one up at your local military surplus store for $1. Therefore, it became "audiophile chic" to "make equipment that was built like a tank - because it was made with parts from a tank". In some cases, the performance was actually excellent; in others, it was simply an affectation. It was cliche that "military equipment weighed a ton, cost a fortune, and lasted forever". This was certainly not a problem - but it did lead to many situations where a massively overspecified part was used, not because it helped anything, but "just because it was there". (People would, quite literally, acquire a set of big radio tubes, or a set of fancy capacitors, or even a complete power supply module, then look for a project where they could use them. For example, 20 uF/600V Pyranol capacitors were often used because they were a very commonly available value.)
3)
WARNING! Very few modern "standard" oscilloscope probes are rated to tolerate over 600V; and some probes used on modern digital oscilloscopes are only rated for as little as 50V; if you try to use them on the sort of voltages you will find in an electrostatic speaker you WILL burn them out or damage your oscilloscope. You will also find that many super-high-voltage circuits, like electrostatic bias supplies, operate at extremely low current and extremely high impedance. Therefore, even the relatively high impedance of a standard probe will load them impractically.... (A typical x10 scope probe has an impedance of 10 megOhms... the bias output on a typical electrostatic headphone amplifier has a 50 megOhm or higher resistor in series with it.) Real high voltage probes have an absurdly high impedance which won't unduly load down this sort of circuitry. (And they aren't terribly expensive; note that you only need a DC probe for measuring a bias supply.)
4)
The impedance of a capacitor drops with rising frequency.... following the well known formula: Xc = 1 / (2piFC)
Xc is the capacitive reactance (in Ohms)
pi is the constant Pi (3.141592654 ..... )
F is the frequency - in Hz
C is the capacitance - in FARADS (not uF)
(it is never zero... but halves every time you double the frequency or the capacitance)
Single electrostatic panels follow this equation quite precisely.
Once things like crossovers and transformers become involved it becomes rather more complex.
Most normal amplifier designs DO NOT operate well into a purely capacitive load (so slightly different designs are required).
5)
Large flat panel speakers do tend to be directional at very high frequencies - and so some people may choose to EQ them (this is true equally for electrostatics and planars like Magnepans).
However, most large electrostatics solve this problem by using multiple narrow panels in a curved array, or using some sort of curved panels, or using separate narrow panels for high frequencies (there are other solutions).
Electrostatic headphones tend to have a small area, close spacing between the various parts, and a single driver per side.
Most electrostatic headphones operate with between 300V and 650V bias - and most headphone amps deliver several hundred volts RMS of audio signal (many operate differentially, from a supply in the 1000V range).
Most electrostatic SPEAKERS have a much larger area, but also wider spacing (for various reasons).
The wider spacing, and the need to move more air, necessitates higher bias and drive voltages.
Most electrostatic SPEAKERS operate with a bias voltage in the 2000V to 3000V range, and require audio drive voltages in a similar range.
6)
Capacitors DO NOT dissipate heat; an ideal capacitor dissipates no heat and consumes no power.
You may put voltage across it, and current will flow through it, but they are always out of phase.
Real world capacitors may get warm - to the degree that they stray from being perfect capacitors (the most common cause is ESR - equivalent series resistance).
However, as it turns out, most electrostatic speaker and headphone drivers are very near perfect capacitors.
Some tiny amount of power is actually consumed moving the air; and some time amount is lost due to ESR and dielectric losses.
The vast majority of the power that is actually consumed as heat is consumed in the amplifier.
(You will find that, if you design a tube amplifier that is capable of delivering several thousand volts, and several hundred milliamps, of audio output, it's probably going to end up big and heavy.)
Now you're trying to say that designing an amp that is flat is harder to do than one with rolled-off high end??? Nonsense! And then you say headphones exceed the requriemenst of speakers for drive in the HF range? Again, nonsense. Electrically, that cannot be. The impedance of an electrostatic speaker drops to below 2 ohms at high frequencies. The impedance of electrostatic headphones is nowhere near 2 ohms....it's more like 20K or higher! With a tiny capacitive reactance or 150pf? Why, on earth, is that hard to drive? You're theories defy physics.
You should re-read the above. You just said the electrostatic headphone amp needs to be the size of the Sanders amp, but only not the size of the Sanders amp. You're counteracting yourself. Which is it? I can't be both. And again, where's all that power going????
Hogwash. I have the right probes in my junk box. Several copies.
Please state the model number. Standard Tek 10X probes would be just fine.
Sorry, this is also nonsense. You should work with RF for a while, and get used to working around 100mHz or so...then get real. It's all measurable.
Why do you think a capacitor doesn't dissipate heat? Unused power is converted to heat. Always. Make the load capacitive and it changes how you calculate it, but it doesn't get converted to acoustic energy, and it doesn't just vanish. Remember, conservation of energy? It all can be accounted for. It has to be. Sorry, that's physics.
However, the reality is, you're not dumping 70W or so into the drivers, they are far too high impedance for that. They're handling likely about 2W, possible 5W tops. Look at the impedance of the drivers your working with. And most of that power is lost to heat because you're not shoving 5W at your ears at close range without permanent damage.