Am I imagining that you used to be able to Multi room to non Naim devices using the.Naim app and Airplay2? Or must I have been using Apple Music? It was a good few years ago last time I did this.
You can mix any Naim or non-Naim streamers in a multiroom group using Airplay, Chromecast or Roon. Naim’s own multiroom controlled from within the Naim app is only for Naim streamers.