Jim,
I have never tried that configuration, but using a Signalink is standard for all rigs:
do not connect to the head, connect to the MIC jack of the control RRC instead.
Also connect the SP jack of the RRC for audio. You can basically program the RRC
using the red straps to use any type of microphone cable (with RJ45, but I would
assume you just use the IC-7100 microphone and a Signalink cable for that rig.
73,
Mitch DJ0QN / K7DX