I’d suggest OP is having issues as Roon is trying to run a multicast session in it’s local subnet and you don’t have PIM / IGMP snooping or similar set up to enable multicast routing over a L3 subnet boundary.
I’d be against pumping the audio over a network boundary by routing it unless absolutely necessary. The Unifi routers like the Dream Machine are software based routers and pumping traffic over a network boundary all hits the CPU.
While you might have enough headroom on the firewall / router from a CPU perspective, I’d consider the Roon core to be more akin to a server in your network and keeping it local to the devices accessing it should be your goal from a performance perspective.
I’ve not tried to get Roon multicast RTSP happening over a VLAN boundary. While it may work, you’d need to do some tinkering.
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