Mixing Ethernet Cables

https://www.bluejeanscable.com/store/data-cables/index.htm

https://www.bluejeanscable.com/articles/is-your-cat6-a-dog.htm

good reading to get smart on the subject

Would running Cat 8 from the switch to the streamer be of any benefit given that the signal is only Cat 5 from the router to the switch?

No.

Unless you are at a national lab doing some huge data intensive movement, or running pornhub, your bit moving demands have been working well 25 years for the reason that it was designed to work.

You might want to look into a Goggle MESH network. The nodes feed ethernet cable to the components. Our router is upstairs, the Mac Mini server that runs Roon core is downstairs; one streamer is upstairs, the other downstairs. The sound quality is excellent. The streamers are Ayre QX-5 Twenty and ultraRendu with Ayre QB-9 DSD DAC. Files Roon shows as 192/24 or DSD are played as that by the streamers.

db

First, see if you can fix up your wifi.  Get a phone or PC based Wifi analyzer app, they are free.

Try to pick the least used channel.  If you can use 5 GHz that's usually less congested and higher bandwidth.

Thank you all.  You've been very helpful.