At my school, we have a Clearcom Partyline system. I was wondering if it is possible to convert a pair of headphones (listen only) to xlr and plug that directly into a Clearcom XLRjack coming from the main station. What would have to be done to make this possible?
Whether or not it would work, the approach proposed is inadvisable. The PL system is designed to operate with a local amplifier in each beltpack and adding a direct load onto the line would likely load the audio line to the point where it's reliable performance could not be guaranteed.
If however you can get a headphone amplifier of some description, you can safely feed the input of that from pin 3 of the comms line, with pin 1 as it's ground reference. You may even be able to source / design an arrangement that could be powered from the comms 30V line.