Ethernet cables

My attitude towards cables, particularly digital ones, is to go one step up from the basement, but not to go into the stratosphere 

They absolutely make a difference and as mentioned should be commensurate in quality to the rest of your system. The "zeros and ones" argument is a false one because the issue is with noise on the line - if not removed - will travel to downstream and present both noise and timing errors for the streamer and DAC to cope with.

Ditto the first answer.

Triode Wire Labs freedom. I have two, one from extender to optical isolation and a very short one from switch to streamer. It gets complicated but it all makes significant improvements.

Everything matters.  A While back, Jay of Jays Audio Lab said to save the Either net cables for last because they made the least amount of difference.

Take it with however much salt you wish.

No, no it's not worth it. Ones and zeroes don't know nor care how they travel and all the stupidly expensive cables absolutely will not change that.