Giant1, I have experienced exactly the same problem as you. I have ALL of my music on a Seagate Goflex Home 2TB network harddisk working as a UPNP server. I have connected it to the SM6 via ethernet cable to make sure those hi-res files don't run out of bandwidth Sometimes, I would even say very often, the SM6 looses the connection or can not find the server even though the server is still visible from my computer or when I check connected devices on my router's admin-site.
I never have trouble connecting to internet radio, playing from usb, coax, toslink, bluetooth (yes, the amount of inputs on this baby is great).
It's really annoying but I don't know if the SM6 is faulty or if my UPNP server is the problem.
Another problem: When I set the SM6 to connect to the network via cable, I can't use the iPad app to control it. The SM6 simply does not show up as a connected device.
Still, the sound is great. The build in DAC is really good and the versatility is very impressive. I use a cheap coax connected Pure Audio cradle to connect iDevices squeezing 320 kbps Spotify files into the DAC.
