And on an unrelated note, the list of file formats 'collectionable' might be missing some rarely used ones, here's what's the Calibre plugin checks:
VALID_EXTENSIONS = ['azw', 'azw1', 'azw2', 'azw3', 'mobi', 'pobi', 'prc', 'tpz', 'txt', 'pdf', 'pdr', 'mp3', 'aa', 'aax', 'cbz']
That should add Topaz, Print Replica, Newspaper/Magazines, Audio & Audible stuff, and Comics. Granted, the Audio/Audible/Comics stuff is useless on a K5.
. (The proper list of supported stuff is with the mimetypes in /var/local/appreg.db, IIRC).