In the Zune software settings, just monitor the folders where you keep your Music.
If you want your playlists in the Zune software as well, you can export your MM playlists, then scan them in with the Zune software. In MM, go to Tools | Scripts | Export all playlists. Export the playlists to somewhere that you'll remember. Then, from the Zune software, just scan that same folder where you exported your playlists (in the settings, add a new "Music" folder). After that you'll have all of your music and playlists that you have in MM. You can even run the script periodically so that your playlists are updated (it will overwrite the old exported playlists). You could also install the Backup
script, which has an option to export all your playlists every time you start up or close MM.