Tom,
Electrostatic headphones use a very, very thin and low mass membrane, positioned between two stators that are driven by a high voltage signal. (The stators operate push-pull to ensure the membrane reacts in a near simultaneous move to the coming signal.
In effect, the membrane reproduces the signal, covering all frequencies fed to it, in a near-instantaneous time.
What this means is what you hear (for example) is what the CD spinner/DAC feeds to the headphone does not have the differences in both the reaction time and the physical distances in space that define a normal speaker system.
What you hear is essentially what the recording engineer and the manufacturer put onto the CD.
I've been using Stax headphones and amplifiers for years to "audition" every classical CD in my collection. (now using the 009 and associated amplifier)
Yes, an electrostatic can sound thin in the bass - - but very clean and precise, and the higher frequencies can appear bright - - but the accuracy and resolution cannot be beaten by dynamic cans, nor the arrival of complex sounds from my 2.7s. (and, no room effects! :-) :-) :-) )
I use my Thiel 2.7s for musical enjoyment. My Stax for finding out whatinthehell really is on that CD.
George