See the following post. I can move the thread to #tinkering if you like since this isn’t a supported configuration but there are some who have got it working.
Hello @John_Hoogeveen ,
I have moved this thread over to "Tinkering’ since as I have previously mentioned, Roon is designed to only support a single subnet for both control and audio streaming. There may be some users who have gotten their setup working on two subnets but we do not officially support multiple subnets and I am not familiar how stable it would be or what exact steps you would have to take to get it working. Some other threads that might pique your interest in subnet configurations…