First you need to find out what tags the software's using. So go into MC and select a file that has been tagged by the two software. Press Tag in the Action Window (bottom left). In the Tag window, right below the Tag title, click the fist line of info (contains file type - duration - size of file). This will show you all the tags in that file. Scroll down and find the tags that your software's using and write them down.
MusicIP might use the following (I think):
MusicIP_PUID
MusicMagic Data
MusicMagic Fingerprint
MusicBrainz uses the following for flac:
MusicBrainz_AlbumArtistID
MusicBrainz_AlbumID
MusicBrainz_ArtistID
MusicBrainz_TrackID
MusicBrainz uses the following for mp3:
MusicBrainz Album Artist ID
MusicBrainz Album ID
MusicBrainz Artist ID
MusicBrainzTrackID or MusicBrainz Track ID (which ever it is MC can't seem to read this tag but I have had other software read it)
Once you know the tag names, you will need to create them in MC.
Tools > Options > Library & Folders > Manage Library Fields > Add New Field
In The Name field you MUST copy the name of the tag exactly (capitalization doesn't matter).
Display = can change to what every you want to make it easier
Display (plural) = same as above
Flags = Music
select User date
Data Type = String
Edit Type = Clear Only (this will prevent you from editing the field yourself)
select Store in file tags (when possible)
close the option windows when done and go to your library and select all the files.
Tools > Library Tools > Update Library (from tags)
If you have a large library this may take some time. You might want to do them in small batches.
If you want to see if it worked just add the tag columns.