And this how the wiring goes. There is no concern for using a straight TRRS to TRRS cable, because the R2 from DigiRig in default configuration is disconnected. So the R2 wire in the TRRS to TRRS cable will doing nothing.
P.S. The GND (sleeve) on the audio side of DigiRig should connect to sleeve on the 2.5mm jack on the uSDX side. My bad, editing the image for the CAT part.