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.
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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.