Hi, Nstream stores the playlist on the iOS device (iPad, iPhone, iPod). You can save copies of these playlists for back up and restore quite easily.
To do so, connect the the iOS device to a Mac or PC running iTunes, select the iOS device within iTunes, go to the Apps tab, and scroll down to 'File Sharing'. Here you will see the nSttream (as well as probably other of your app logos). Click on nStream and on the right hand side of the screen you will see all your nSteam stored playlists. You can select them and save them etc.
But bear in mind, if your uPnP server programme builds a new database or your NAS changes IP address or path to file shares, then these playlists will not find the referenced file, and nStream will show a little red cross by the play listed media.
Simon