I believe the 210 is not just a UPnP endpoint but also a server so it can serve files to itself, just connect a hard drive to the USB port on the back, not sure about the control but assume it is through the app supplied with the 210.
So depending on the setup no PC or NAS is required, depending on your library size of course.

Shame the 210 spec didn’t include USB out or analog out, or that they didn’t include the Bluetooth, Spotify, RAAT support into the existing 218/251.