Based on the above mic schematic, the audio cable for Digirig will look like this:
GX??-6 pin 1 (Modulation) → 3.5mm TRRS ring 1 (RIG_AFIN)
GX??-6 pin 3 (TX) → 3.5mm TRRS ring 2 (RIG_PTT)
GX??-6 pin 5 (Ground) → 3.5mm TRRS sleeve (GND)
3.5mm TRS tip (Ext. Sp.) → 3.5mm TRRS tip (RIG_AFOUT)
Connection GX??-6 pin 2 (RX) → GX??-6 pin 5 (GND) may also be required.
Please report your results if you give this build a go.