Headset wiring for Buzzcom intercom

[D2O]

I currently have 1 buzzcom headset for my plane (2 jack type).
I want to convert another buzzcom headset (single jack type) to a 2 jack type to work with the intercom for pax, and have traced the wiring, but have noticed the 2 jack type headset has a mic pre-amp installed in the headset, while the other headset does not. Is this pre-amp necessary, or is there already a mic pre-amp in the buzzcom intercom box?
Has anyone done this conversion before?

[mulderpm]

Phone Larry Eschner. Zero ate too for 1 oh one five three too.