to use it a s a Music Server to conect it to a coax cable and feed a DAC? or is there any other more elegant option to connect a Mac Mini to an external DAC taking into account that my DAC does not have an USB port???
The Blue Circle Thingee will take a USB input and output coax as well. Of course you can always go digital out (mini toslink) to toslink in on your DAC if you have that facility. I've used both and preferred the Toslink, but that's just me :-)
Also Tascam in the Pro-Audio world has a USB device that has SPDIF out. They can be picked up at most GC type stores. The last time I looked for one they were about $149.00. I believe the model number is US424.