The UPnP specifications for NAD C 338 are based on Chromecast abilities. Chromecast devices can play music from NAS via UPnP/DLNA apps such as BubbleUPnP or UPnP Monkey. These apps are officially supported by Chromecast.
Reach out to Google for further information on how to connect a Chromecast device to NAS via UPnP using the above-mentioned apps.