Mcintosh mc240 and headphones possible or not ?

Paul,
There is a website for Stax:
www.stax.co.jp
which has a history section that shows old products.
That is the main thing, that these are older models. The new driver units seem to be small amplifiers themselves. I am not expert enough to know which old model might be best or how you might find one. They are driver units for their own headphones. The SRD series seems to be the driver unit that hooks up to your own amplifier. I will confirm my model tonight, but I believe it is the SRD-7. There are a couple of listings here on Audiogon.
Good Luck,
Bill

Paul,
I checked. I have the SRD-6SB (self biasing) version.
From their description:
Different from the low-impedance type conventional dynamic headphone driven directly by the amplifier output, STAX electrostatic earspeakers are high impedance type and they call for high voltage to drive. The function of the SRD-series energizing adapters is both to transform the amplifier output to this requirement of the earspeakers and to provide the polarizing voltage to the diaphragm....
(more in their PDF)
There are also big differences in the earspeaker models themselves. I like the Sigmas, but I have not seen them available, nor have I heard the newer models.
Bill

Thank you for doing the research,,you should post your rig would be interested in seeing it. Bye thanks again Paul