Besides connecting a USB HDD to your Meridian 210, Meridian recommend alternatively installing BubbleUPnP or Audirvana on your Mac.
On watching this Hans Beekhuyzen
video, I installed the modestly priced FireStream from the Mac AppStore. This enabled my Mac Mini to act as a UPnP Server.
On launch, FireStream instantly recognised my Meridian 210. Besides running Logitech Media Server on my ReadyNAS, I also happen to have the LMS app on my Mac Mini.
On my iPad, by trying both Arcam’s MusicLife, and mcontrolHD, it was simple enough to stream music from my Mac Mini to my Meridian 210 (via LMS).
This is no better nor worse than installing/using Audirvana for MacOS/iOS - except for the almost £90 price tag (compared to zero cost for MusicLife or mcontrolHD).
The caveat is that while Audirvana doesn’t like other UPnP devices being present during operation, FireStream isn’t similarly troubled by other UPnP devices being present.
Then again, most users will be sufficiently content with the 210’s connected HDD as a UPnP Server.