An excellent paper on routing cables to avoid interaction and noise injection.

     Was there something to read, in the original post? Didn’t show up, here.

     At any rate: if one considers the low voltages/currents we’re dealing with, as regards the typical system’s interconnects; the Inverse Square Law works nicely, with a few inches distance, when faced with parallel runs.

     AC cables and interconnects (particularly so, if unbalanced) may prove another story; especially, if the interconnect feeds a higher gain circuit (ie: phono).

     Crossing cables of any kind, at 90 degrees, is sometimes the only option and will typically avoid induced currents.

               http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/isq.html

     https://www.thepodcasthost.com/equipment/cable-crossing-bad-thing/#

     "I discovered any low level hum at all dissolves clarity and definition, even at louder volumes*, so the long effort was well worth it."

                                           *I couldn’t agree more.

     If I'm not mistaken: the better Stax headphones/amps work at much higher voltage levels than most, which could (possibly) account for the distances necessary, from your other components.

                   KUDOS, for persevering and lowering your noise floor!

                                      You're welcome.

       Regarding the Stax pieces: I was thinking about the bias and signal voltages, that some of their amps supply to the electrostatic phones (little current/big voltages, relatively speaking).

                          ie: https://staxaudio.com/technology

                                       Happy listening!