If I'm successful with that I will post a utility for that, although many people have upgraded the dual core Xeons in the 2006 to quad core Xeons without any ill effects, so I don't know how important this really is. The SMC version will stay at whatever version it was at before the update, and I'm looking into a SMC firmware tool, as it is also an EFI program that runs during the boot process. Everything is left on the RAM disk for you to look at and study, if needed. The program creates a small RAM disk, downloads the needed files, copies all of the scripts to the RAM disk, and then runs the scripts.

The download does not contain any firmware updater files or image files. If you have a 2007 Mac Pro, the program will warn you about downgrading, but will still allow the firmware update. The program checks the Mac Pro model and will only install the 2007 Mac Pro firmware on a 2006, or the 2006 Mac Pro firmware on a 2007, whichever is appropriate. If you have a CPU or CPUs in a 2007 Mac Pro that isn't supported in the 2006 Mac Pro, the system will not boot after the update until a compatible CPU or CPUs are installed. I have tested this myself, on a 2006 Mac Pro.