FWIW, this is my arrangement with a GM300 modded to 32 channels and a URIx.  Without the influence of the URIx the radio always reverts to the last channel set by the CHANNEL button, not the one set via steering.  I have not had occasion to test that in a brown-out circumstance.  Regardless, initial channel after reboot is set to #1 by simpleusb.conf, snippet below.  Note there are five lines available from the URIx and five available on the radio via S/W.  I have not yet bothered to define the last 16 available.  While all this seems to work fb on the bench, there will be a camera pointed at the radio display when deployed to the mountaintop in a few days.  I hope this helps someone and that my approach is not too backasswards.