Just found what I was looking for here
FAQ:
What file formats are supported?
Windows
.aiff – full tagging support too!
.m4a (AAC)
.m4a (ALAC)
.mp3
.mp4
.flac
.wav
.wma
Mac
.aiff – now with full tagging support!
.flac – though we still recommend alac for Mac users
.m4a (AAC)
.m4a (ALAC)
.mp3
.mp4
.wav
Can I import my collections from MIK 4?
Mixed In Key 5 has several new features that require files to be reanalyzed. Chief among these is upgraded key detection. We always recommend that key results from any algorithm only be used with other key results from the same algorithm.