I have a small separated network for audio.
It consists of a small and plastic Linksys wifi router connected to a Cisco 8 ports metal housed switch. (Nothing fancy.) Also have a Synology (DS118) one bay NAS with SSD and running Asset on it connected to switch. My NDS streamer connects to this switch as well. My hifi is on dedicated spur while this network uses the ‘ordinary’ power circuit of the house. I got rid of all switched mode power supplies which came with router, switch and NAS originally. Changed them for a small Mascot made linear power supplies in the case of router and switch and an Sbooster LPSU for NAS. All 3 needed ethernet cables (from router to switch, from NAS to switch and from switch to NDS) are Meicord opals now.
Some jump in SQ was experienced by changing all SMPS to LPS in my case. Changing from HDD to SSD has also positive effect on sound but to a lesser extent in my case again.
It would be worth trying a cable like AQ Vodka from switch to NDS. A friendly dealer should be able to loan you a cable. Others have bought ethernet cables from blue jeans cables, and liked what they have heard.
if fully separated , there is probably not much you can do… and you won’t benefit from IGMP snooping.
However you have a first gen streamer, these were sensitive to inter frame timing consistency of the media transfer from the media server. Therefore you might find changin the UPnP media server platform beneficial. I found the best platform suprisimgly was a ReadyNAS RN202 running ReadyDLNA.
I found general compute platforms such as iMac and RPi the worst in this regard.
BTW most consumer switches use DC to DC converters inside so they they have small internal SMPS operating irrespective of what you are using for the main powersupply.