I HAVE SOME GREAT REASONS WHY NOT TO DO WHAT YOU WANT TO DO.

The first thing I would suggest is that you DO NOT USE XLR's for headphone connections. You wouldn't want to have somebody mistakenly plug any of your microphones into a power amplifier output. There are plenty of connectors that utilize the same form factor as the XLR's that contain a single 1/4" TRS connector jack. Companies like Neutrik, whirlwind and others make those.

You also do not want to share a common ground between the output of a headphone amplifier and your microphone input shield. So you want to make sure you do not connect your microphone input connector pin 1 to the metallic case of the connector or front panel, that would make its ground common to your headphones connector.

Utilizing quality microphone snake cable such as the MOGAMI or Canare line of products is perfectly adequate for your microphone inputs but again, I would not try to connect a power amplifier headphone output through the same snake cable as the signal can become inductively coupled to the microphone inputs since the snake cable is essentially a large linear winding of an air core transformer. Make your headphone feeds to your panel from separate 3 conductor AC zip cord. Like the kind you find at the hardware store and on those orange extension cords, that are at least 18 to 16 gauge. That is the only kind of appropriate wire used for power amplifier outputs. I can't tell you how many idiots I see using small gauge shielded microphone cable to connect speakers to their power amplifiers! Many amplifiers will blow up and fail from that kind of wiring due to its increased capacitance. Power amplifiers generally don't like to see a capacitive load. Another reason why special amplifiers are utilized for electrostatic speakers. You don't want to use those either in a control room recording studio environment (I considered them for my remote trust due to the space savings such as you find these days in LCD video displays), such as the Quad's, as they really don't play loud enough before an electrostatic spark, passes through the membranes, often rendering the speaker unusable.

Next, you will probably also want to build individual headphone boxes and be feeding them from a " 1/4" break out box" with passive distribution from a single power amplifier. I have posted numerous posts about how to build this incredibly easy, rugged and personal headphone distributional system without purchasing those stupid rackmount 4 output " headphone amplifiers". Those are only adequate in the control room of a bedroom project studio and rarely sufficient when trying to track an entire rock band. Your headphone amplifier should be something like a Crown D60/75 or equivalent. Provided it has adequate output transistor protection circuitry. Old used amplifiers like the classic DYNACO's rarely survived as their output protection only helped to limit current to the speakers and in the case of an open or shorted connection, you could guarantee yourself a thoroughly blown up unusable amplifier. Suitable for burial purposes.

Headphones R Us
Ms. Remy Ann David

Thanks for the suggestions. I will plan on one box for the mic inputs and another one for headphones. I already have a crappy rack mount heaphone amplifier, but it works well enough for our needs.