Thanks for providing more info on your router. By eliminating cheap stock wall warts, you have already improved performance of your router and modem. For now, just hold off to upgrading the router and streamer and work with what you’ve got on hand. I like the idea of choosing a CAT 8 cable for serious listening. Link Up Cat 8 cable is a very nice high quality cable with an option to return if you don’t hear an improvement. I’m currently using an 22AWG version which is bit stiff ahead of a $5K switch from my modem. The 26AWG version (blue) is lot more flexible.
Try it with LHY, let it settle down in your system before forming any opinion. If you feel there is no net gain then trying a better streamer from Aurender or Innuous would be the next step. They have many offerings, pick one up based on your budget.

