Hi @filorus,
You cannot specify an IP address for the endpoint unfortunately. The way that this works is Roon sends a multicast broadcast packet to the network to identify Roon Ready devices and the Roon Ready devices respond to this request and then become visible in the Audio section.
If something is preventing the proper delivery of these packets, such as a firewall or issues with the router’s configuration itself then this is why the Roon Ready device does not show up there.
I also had this other TotalDac case a while ago that may be useful in troubleshooting here: (Router change causing problem). The solution for that case was to add a network switch in between the Dac and the router, so this may also be an interesting aspect to check.
– Noris