@plhought How interesting that the ground comm functionality evaded me (and all the descriptive manuals, from what I could see), despite how many details I have learned about this aircraft. You are also correct about the avionics relays functioning the same as a King Air. I was also looking at section 24-56-00 in the wiring diagram manual, but my rush to answer before Flight Sim Expo must have gotten the better of me.
I will add the ground comm functionality immediately. Do you have a page/section in the wiring diagram manual for the ground comm switch? I would assume that the master battery switch also closes the same connection between the RTU1 + COM1 transceiver and the hot battery bus, such that the ground comm switch could be released after the battery is connected, and the RTU1 + COM1 will remain energized.