My understanding is that ethernet cabling and switches powered by smps etc. are noisy and can adversely affect the circuits they are plugged into. This has nothing to do with the digital packets and how the network hands them off to the streamer. I recently implemented the optical ethernet conversion for around $200 with an ifi power supply for the last converter. Made a significant difference to my ears.
Improving Digital Streaming with a Gigabit Ethernet Media Converter System – PS Audio