Thanks for the update. IME, ROON implementation is one of the main reason why end user would experience inconsistency in SQ. Every manufacturer or designer doing their best to integrate ROON and tweak their hardware for best possible outcome. As @audphile1 pointed out, ROON SQ greatly varies due to the approach in the implementation by each manufacturer. Some manufacturers excelling and others couldn’t care less as long as they are meeting the ‘ROON endpoint’ specifications.
Coming back to your system, If I may make a suggestion to strategically introduce each change one at a time. Starting with LinkUp cable, let it break-in for atleast 250 hours before you introduce next upgrade, i.e. LHY switch. Once all the components are fully broken-in, then reverse the process for A/B comparison. Listen for extended periods, especially LAN cable. Streamers typically buffers or cache incoming bitstream so swapping LAN cables on short intervals may not allow you to discern any differences.
Good luck and have fun!