The UPnP AV streaming server software needs to support WM-DRM, which I doubt your NAS box does. PVConnect (Twonky) definitely doesn't. Heck, even Windows Home Server doesn't officially spport content authentication like this. Also, whatever is serving it also needs to have the Zune software installed, since that's the only method to login/authenticate the content to the Zune ecosystem at this time.
So, the best you can do is to mount the network content on a running Windows system... and use that to "re-serve" the content. (Windows Media Player or Zune's network sharing service.)