Stax headphone amp with non-Stax headphones.

Also, its not a balanced (XLR) connector. There are 4 pin and 5 pin (aka Pro) Stax headphones, but its not a 3 pin XLR.

It's 5-pin balanced connector with shared ground that is used in Stax amps. Every amp is designed for a specific load(impedance). I would doubt that impedance of electrostatic headphones is in the single digits(aka ideal for iPod)

If by "non-Stax headphones" you mean "non-electrostatic headphones," don't even think about it!

As Elizabeth indicated, electrostatic headphones work at VERY high voltage levels, which are sourced from high output impedances. Dynamic headphones are the opposite, requiring low voltages sourced from low output impedances.

Also, if the "shared ground" you are referring to is the non-signal pin on the connector, that is the bias pin which is probably at 580 volts DC relative to the zero-signal level of the audio outputs. And I believe that the zero-signal level of the audio outputs may in turn be offset by a large voltage relative to AC neutral and AC safety ground.

Regards,
-- Al

WOW,
Thanks all,
The Stax connector is the same as 5-pin stereo-balanced connector with "slight" difference:-)
I've seen some balanced headphone amps with the same 5-pin connector