Intercom box came in today. Went out with my headset plugged it up to the car and it works as advertised. Still need to pick up a high to low impedance adapter for my 2nd headset and install the box in the car. I've been putting off getting that second adapter so this'll motivate me to pick one up on Monday.
Fidelity isn't as good with the aux input (iPhone) as I was hoping for but will work good enough for my tastes in the car and with the sound attenuation of the headset.
I'll do pics after the install.