FWIW,
I have analyzed streaming downloads from Tidal while playing items in ROON.
Roon will download a song and begin to play and will download at least the next song while the current song is playing.
For much of the time that a song is playing, there is no/minimal network activity coming into the roon server., except when pre fetching the next song in the queue, which may only take a few seconds to a minute ( ISP download speed dependant). As such, im not sure that having a separate line, or high quality of service from the ISP would make much/any difference. As far as I can tell, the song exists only in memory once it is downloaded and waiting to be streamed.
A server on a lan segment will experience a CPU interrupt for each broadcast packet, multicast packet or directly addressed packet that it 'sees'. Also, as the traffic itself, must introduce EMF/EMI into the server thru the ethernet port, it is good to limit the amount of traffic to the server. For this reason, I have setup my server on its own VLAN and separate routed segment. This will limit the amount of traffic that the server needs to process to only packets addresses directly to the server from the firewall/router which is passing traffic to the server from tital/qobuz amd will eliminate the broadcast/multicast packets that are being generated but the devices throughout the rest of the house.
I would also suggest creating a back-to-back ethernet cable network between the Server and Ethernet DAC for the same reasons. This will keep the DAC from having to process spurious traffic which is seen by having the Ethernet DAC plugged directly into the network used by the rest of the house. Your music server will need to be setup as a DHCP server to offer up an IP address to the DAC, unless the dac can have an IP address set manually. My lampi Pacific dac needs a DHCP server (for example).