for USB cable, yes it does matter to the sound quality. I have 2 types of USB cable for my dac, 1 is iFi Mercury3.0 OFC cable. the 2nd one is custom 4N pure silver 8core USB cable. both improve the sound quality with different character.
For Ethernet i only have experience with better power supply for my Wi-Fi router, it also gives sq improvement after install the iFi iPower-X power supply. I think the Ethernet cable will do the same to improve sq.