I know im behind on my firmware update myself but my Mackie Control MCU is working fine within sonar.
FYI- ive been looking for one of the original extenders forever (the C4).
I was a bit concerned about the firmware update as well but it hasn't stopped me from using it with Sonar and using almost all of its functionality.The Mackie Control within Sonar is great.
Have you had it hooked up and using it with Sonar ?
And is it, do you have an issue with the extenders ? that could be to do with the MCU and the extender themselves.
For what it is worth, the upgrade is in the form of a chip I believe. The newer ones can update through USB.
But our units, the older ones are midi.