Based on above pinout the Digirig audio cable will look like this:
RJ45 pin 1 (MIC) → 3.5mm TRRS ring 1 (RIG_AFIN)
RJ45 pin 2 (GND) → 3.5mm TRRS sleeve (GND)
RJ45 pin 6 (PTT-KEY) → 3.5mm TRRS ring 2 (RIG_PTT)
RJ45 pin 8 (AF) → 3.5mm TRRS tip (RIG_AFOUT)
The good approach would be to use one of the existing shielded/choked TRRS cables and crimp on the RJ-45 jack on the transceiver end.