Speed kills....

I was just thinking, if we want to talk about the benefits of the ESL as a driver, maybe we shouldn't compare them to box speakers, but dipoles and line sources instead. 

That is a much more fair comparison of the ESL's quality than in a conventional box. You get very similar dispersion patterns (but not the vertical narrow control) 

Yes Erik, absolutely. ESL’s are almost often implemented as dipoles (sound launched forward and rearward), but not always as line sources. None of the Quads are line sources, but all are dipoles (though the rear of the 57 comes covered in felt---the center tweeter---and burlap---the entire back of the speaker). And of course a line source can also be made with multiple cones or domes, and as either a direct radiator loudspeaker or a dipole.

Duke,
You work in an interesting way and present what you do quite convincingly. I wish you success.

I don't know why Duke introduced Stax headphones; but that was exactly what I thought when I read the OP.  Is there any way you could audition them, Russ? 

???
2channel8: I have the Lambda headphones with an SRM-1 (mark2, I believe) amplifier.  I'm trying to replicate that sound but on a larger scale.