I go by empirical results - what works, works!
I suspect the CAT7 screen forms an electrical connection that does not add to audio SQ but adds noise along the screen between the cases being connected by the cable. Without the screen there is more isolation.
It is about perspectives - Ethernet screens are to protect the digital signals from cross-talk and other introduced noise and not intended to have any HiFi benefits other than possibly reducing noise from the Ethernet cable radiation and getting into other cables.
I’m suspecting it is more complex and that increasing HF edge rise-times actually could increase radiated noise. faster edges are great for higher-speed transmission but you don’t need this with the connection to the ND555.
I’ve got some ideas from trying the CAT7 and CAT6 to the extent that the CAT6 was better than CAT7 and had some better clarity than the old CAT5 I used but also introduced an emphasis towards the top-end I found fatiguing over time and detracted from LF timing and sense of ease in the presentation.
I’ve heard similar effects when auditioning loudspeaker cables of different lengths and the shorter runs were brighter and ‘shouty’ whereas the longer runs of 5m or more were far more neutral and still longer runs seemed just better with better bass articulation.
I’m not saying it will be identical with Ethernet cables but I suspect the 0.5m of CAT6 I tried was too short and a longer run may work better - it is not expensive so I will try it in the next few days. I recall Naim doing a lot of testing on getting the right lengths of interconnection leads as there seemed to be optimal lengths for sound quality - with no obvious reasons given what would cause any differences.
I have tried HiFi Ethernet interconnects and may try some more and if they work then that will be great. But I suspect I may also prefer a different and more neutral presentation to many, as these cables all seem to have a ‘character’ to them I’d not call neutral and tending toward or overtly too up-front presentation and obliterating low-level detail in background acoustic.
The ND555 is very revealing I’m finding and getting the right interconnects seems a good idea.
I remember in a Naim demo of ND555 at my Dealer Naim were emphatic about NOT using any special cables and only using standard Ethernet leads - I now understand why.