Based on the above Digirig’s audio cable for Yaesu FT-5100 will look like this:
3.5mm TRS tip (DATA IN) → 3.5mm TRRS ring 1 (RIG_AFIN)
3.5mm TRS tip (DATA IN) → 2K resistor → 3.5mm TRRS ring 2 (RIG_PTT)
3.5mm TRS ring (DATA OUT) → 3.5mm TRRS tip (RIG_AFOUT)
3.5mm TRS sleeve (GND) → 3.5mm TRRS sleeve (GND)