I wasn't aware that MC had the ability to import metadata only?
When MC imports media, it just reads the file's tags and its location and saves these to its library.
It's possible via MPL to import metadata, which is an XML format that MC uses and this applies only to media that has not been imported as yet, you can't update metadata for already existing files in MC using MPL.
So going back to the orig posters Q, it's possible but there might be some preparatory work to do.
Need to know what tags are comon between the two apps.
- If you saved (playcounts, last played dates and ratings) to the file, will MC be able to read these tags ?
Try with a few files and see if it works. If not then there is going to be a bit of fields juggling going on to get it to work. You copy these fields to the ones that MC can recognise whilst in musicmatch, then import the media into MC and Move->Copy these fields to their right place. This requires saving these fields to the files.
OR
If you don't want to save anything to the files or its impractical to use fields then export the musicmatch library in a text form, then transform it to MPL format and import into MC. This will require some knowledge of either Perl or XSL.
To see what the MPL format looks like, save an album whilst in MC by File->Export Playlist->Format (MPL Playlist), select where you want to save it and then click OK.