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I wish to thank Jim Gerfin, Charlie and David McGown to turning me on to this. While they are using better quality equipment than I am, David suggested trying the simple $25 TP Link converters along with a 2 meter optical cable, then a 1' CAT8 cable on either end to replace the CAT 8 cable between my ethernet switch and end point/renderer. There is a marked and obvious improvement in sound quality.
This is an easy to try change, it may work for others by creating galvanic isolation between the switch and renderer. Total cost was about $70-$75.
Next upgrades will be linear supplies for the switch, router and converters. Later, I'll spring for better quality ethernet components with better clocks.
A great explanation of what is happening is found in the attached paper. Lots of room for improvement here.
Thanks again!
Stuart