With respect to optical fiber implementations, I've been doing this for a while now, and have found every "control factor" with respect to fiber can and does, have an influence on the audio quality. This includes but is not restricted to:
1) The fiber media convertors (FMCs). The better (audio grade) ones, e.g. those used in Sonore OpticalRendus, Uptone EtherREGEN (ER), SOtM products, Lumin, etc, sound better than the el-cheapo, IT- industry grade ones (e.g. TP-Link, etc)
2) The optical transceivers. In my experience, single-mode (e.g, Planet Tech) sound better than generic multi-mode (e.g. TP-link)
3) The optical fiber: For single-mode fiber, I've found that Corning ClearCurve single mode sounds best. For Multi-mode: Tripp-Lite.
4) The power supplies for the FMCs: generic SMPS sound the the worst, LPS sound the best, including those from Sonore, AfterDark, SOtM, etc.
5) Word/Master Clocks for the Ethernet switches or FMCs that have SFP cages. AfterDark makes a nice range of affordable Master Clocks for products e.g. EtherREGEN and SOtM (ER also has a clock input).
6) Clock cables for the Master Clocks for FMCs: better clock cables also improve audio quality.
7) Power distribution for the power supplies for these devices. Audio quality power distributors bring notable improvements.
8) Ground-plane noise reduction: reducing and/or removing ground-plane noise from these devices can provide notable improvment in audio quality. For example, simply connecting a ground cable from EtherREGEN's ground terminal to a Shunyata power distributor GP-NR terminal, Altaira ground hub or Gemini ground hub can provide a notable improvement in audio quality, even "downstream" for components in the main audio rack.
Could you elaborate on how you came to these conclusions? DBT? No measurements it seems?
Please don’t take this question as criticism, just trying to wade through all theories and statements about networks and music streaming from different sources.