Great writeup OP.
I've done this upgrade as well a few years ago swapping my 2013 M6 steel rotors to a 2014 M5 carbon ceramics with all parts listed as well as coding. We didn't do the iDrive controller at all and I'm not sure why it would be necessary.
I also have the older iDrive as my m6 was a late 2012 production build. Install and coding done by BMW master tech. No issues with the retro fit and has the same brake feel as my 14 M5 with CCB's.