Here's a breakdown of what itunes MP3 metadata maps to what Traktor Metadata...

Itunes = Traktor

Artwork= Cover Art
Bitrate= Bitrate
Rating= Rating
Name= Title
Artist= Artist
Album= Release
Time= Time
BPM= BPM
Genre= Genre
Comments= Comment
? = Label
Track#= Track
? = Key
Lyrics= Key Lyrics
? = Comment2
? = Remixer
? = Producer
? = Mix
? = Catalog #
Year= Release Date
Sort Artist= ?
Sort Album= ?
Show= ?
Season= ?
Release Date= ?
Purchase Date= ?
Sample Rate= ?
Sort Show= ?
Sort Composer= ?
Grouping= ?
Episode ID= ?
Episode #= ?
Disc #= ?
Description= ?
Composer= ?
Category= ?
Album Artist= ?

Info such as playcount & skips were left out as they are only pertinent to the individual programs. For metadata changed within a program, the metadata won't change in the other program until played(in itunes) or loaded into a deck(in Traktor)