Here are some relevant threads on this forum. Plenty more on this somewhat controversial subject onllne elsewhere.
In addition, in direct response your your queries here about basic hygiene:
1. To what extent are music servers impervious to the quality of network inputs/connections?
It seems most are not impervious, some are better at rejecting or filtering out the unwanted stuff that comes in with wired ethernet signals.
2. Can an ethernet/fibre combination ever better an all ethernet set up using (in both scenarios) high quality audio grade network components?
I think fibre is a critical and very cost effective way to create an absolute noise barrier to isolate your hifi from both the rest of your network and also the outside world and things you can control/change (such as the device that terminates your fibre to the premises). FIbre, and SFPS in particular, are a rabbit hole in themselves and it seems it is easier and less audible putting fibre as far upstream from your hifi as you can.
3. High quality audio grade power supplies: which is better suited to networking devices/applications: SMPS or LPS?
Whichever generates the least noise.
In relation to some of the things you have already:
• All my ethernet cable are mass market ones: cat 6a shielded.
Shields are problematic because they are typically connected at both ends to ground and so can pass on noise. As a general guide I suggest:
- long runs should be fibre
- cables closest to the hifi endpoint are best to be ‘audiophile’ variety
- other cables, such as upstream of fibre, Cat 6 or 6a UTP.
a) Separated the mains line feeds for a) home network components and b) 2 channel set audio up.
Good, ideally do not power network devices that are enroute to your hifi with the same power supply.
c) disabled the wifi functionality on the ISP modem limiting wifi to just the mesh wifi set up;
The ISP modem will be a weak point. Get a better router, preferbly enterprise grade. I use Mikrotik, and that is another story. Connect the Mesh router vais LAN rather than WAN so it will still mesh.
d) replaced all OEM switch mode power supplies (SMPS) with 12V ifi ipower v2 & X models.
Good start, others are lower noise LPSs and they will make more dffference closer to the hifi endpoint.
I have already done a fair few other experiments (with power supplies, fibre media converters, Net network switches……etc) and plan a few more.
This is essential, every combination of devices and cables etc is unique, and so are your circumstances and preferences.