If you - wisely - want them to be in two different, fully independent zones then you will need two WiiM Amps.
You can link them to a group whenever you want it, so they'll be playing the same content. When you unlink them they won't influence each other at all.
There are other solutions (using external speaker switch boxes) that would allow you to play the same music to each single one or to both zones. But this would never allow you to play different contents to each zone. And you would lose some power output.