When you setup the zoneswitch, you can use a Search Wizard to help creating the argument that selects the media files for this zone. If the search argument is valid for more than one zone (you want to play music in two zones) things gets a little more complicated.
Have a look in the Search Wizard to see if you can use other values to combine with 'file type' to differentiate the two music zones.
Do some experimenting, it is rather simple to get working. You can see in the Playing Now Overview what is playing in which zone.