Aviation headset test circuit - op amp

I have put together an overly complicated headset tester with hopes to expand it to a intercom station. But it doesn't work as I wish. No mic audio is audible in the headset. I am using a standard aviation headset David Clark H3312 with a 600ohm load.

Have I overlooked something very obvious?

What can I do to troubleshoot the lack of mic audio?

Are you getting around half supply at all the opamp outputs?

Is the bottom half supposed to be a level detector / squelch of some sort, or some kind of bias stabiliser?