@RadicalxEdward: Dual mobi = file containing both old mobi formatting and new KF8 formatting (which is needed to be able to use things like "Panel view"). kindlegen commandline tool (which KCC uses to produce mobi files) by default outputs that type of file.
Java Mobi Metadata Editor should be cross-platform and work on Mac. And if I remember things correctly it handles dual mobi files.
Even better you should probably install "Kindle Unpack" plugin for Calibre and use it to split KCC generated (dual) mobi file to .mobi and .azw3, and transfer the azw3 one to your Kindle. In this scenario you would probably edit metada for azw3 file using JMMM Editor.
EDIT: Blah, I'm too slow