Conveniently the GX16-8 mic connector features audio output.
The audio cable to Digirig will look like this:
GX16 pin #1 (MIC) → 3.5mm TRRS ring 1 (RIG_AFIN)
GX16 pin #5 (PTT) → 3.5mm TRRS ring 2 (RIG_PTT)
GX16 pin #6 (GND) → 3.5mm TRRS sleeve (GND)
GX16 pin #7 (GND) → 3.5mm TRRS sleeve (GND)
GX16 pin #8 (AF output) → 3.5mm TRRS tip (RIG_AFOUT)
Alternatively the signals are available on the accessory port in the back, but it is not clear which pin is for the audio input. Also it may be difficult to source the connector for the homebrew cable build.
ACC pin 3 → 3.5mm TRRS ring 2 (RIG_PTT)
ACC pin 4 → 3.5mm TRRS tip (RIG_AFOUT)
ACC pin 8 → 3.5mm TRRS sleeve (GND)
ACC pin ? → 3.5mm TRRS ring 1 (RIG_AFIN)