m4p and m4a AAC files from iTunes
Apple recommends that you protect your investment in m4p files by backing up your library.
AAC files are the naked audio without artwork etc. It makes no sense to drop those on File Juicer.
M4A files are AAC files with cover art and other meta tags.
Using iTunes libray with Roon
If you are importing your music from iTunes into Roon and have more than one image per album, you will normally only get one image over. Fortunately Roon can handle extra images if you place them in the same folder as the audio files.