Hi @thierry ----- Thank you for the report and apologies for the troubles. We have documented troubleshooting tips specific to PS audio devices listed here for further tips 
To Confirm:
Setup = The Roon server is on an OS X Siera system on a Mac Mini.
- Can you provide the specs of this machine?
The Bridge II is running = PIC (1.8.8) FPGA (112) USB (33) REV(135) Bridge (2.7.11)
- Is the above correct? What version of Torreys are you running?
Connection = The mac mini is connected UPNP to the network as well as the Bridge II/Dac
- Moving forward, can you please expand a bit more on what your network configuration / topology is like as well as giving some insight into any networking hardware you are currently implementing.
Lastly, are you able to confirm that the DS can be pinged from your Mac Mini without issue?
-Eric