I had a feeling my description might have been poorly worded. Sorry for that, I’ll try again.
As part of the setup process outlined in the PDF user guide, I mapped the WD to my PC as a network drive, on mount point Z. Thus I can browse to the hard drive via the network in Windows 7, and see everything that is on it, including the theme files.
When I set up the network sync from within the device interface itself, it created the network map folder on the drive, just as you described. Things then appeared there, files that I could see when I looked at the mapped drive on the network. But none of those files ever appear in the WD library.
Contrariwise, when I manually copy files to the mapped drive - say, Z:\FolderName\SubfolderName\Filename.MP3 - those files almost immediately appear in the library on the WD device. I’m sitting at my computer, right next to the device and the TV, and I’m watching these things happen side by side.
In short: files that network sync, which I can physically see on the mapped drive (when viewed from within windows), do not make it to the library on the device. Files that I manually copy into the mapped drive (via Windows)) immediately appear in the library on the device.
I hope that makes sense. I can’t think of any more specific way to explain it.