Data, if you connect the UnitiServe to one of the digital inputs on the NDX, the NDX no longer acts as a player to the UnitiServe, but as a "mere" DAC. The n-Stream app will still be functional, but you cannot control the UnitiServe's music with it (only inputs on the NDX and, if using RC5 connection between NDX and preamp, volume too).
In that configuration you are using the UnitiServe as hard-disk player -- it's not on the network and therefore cannot function as a UPnP server (for the NDX UPnP player function). The UnitiServe, however, can be controlled with the n-Serve (NOT n-Stream) app. So make sure you've chosen the correct digital input on the NDX and then use n-Serve to select a tune and start replay directly from the UnitiServe. (Also make sure you've chosen the correct input on your preamp.)
It's certainly an unusual setup, not sure how the sound quality compares to one using the UnitiServe as a UPnP server that serves files to the NDX via the network ...
