Hmm. The ¼” to RCA adapter arrived. However, there is no power output when transmitting. Phones are working, and the footswitch (adapter above plugged into the PTT jack) does trigger the transmit.
The headset's mono mic plug is plugged into the rear panel mono MIC jack. So it appears that the 3.5mm MIC connection is not working. I suspect that there is a setting somewhere that is not right.
I have tried MIC SEL set to rP.L, rP.H, rP.L bIAS, rP.H bIAS.