Last couple weeks have a) made a fiber connection to my DAC (Weiss 501); and b) added a Shunyata Delta Ethernet cable to the mix. Using Roon.
Results:
Fiber connection bought off Amazon plus a IFI power supply instantaneously reduced digital glare and made the music more organic. Obvious difference. Investment: $200
Ethernet cable: Provides greater clarity and separation, but in a much more subtle way. Definitely diminishing returns department. Investment: $850 new (I got used for less).
Conclusion (for me): the front end feeding my digital system definitely makes a difference. Fiber is a no brainer; high end Ethernet may not be worth the price.