Interesting findings. In my experimentation/complete overhauling of my copper to fiber LAN, there was never a marring out of details. It was quite the opposite actually. Much better extension, space and micro details when I removed all of the added distortion/noise from the infrastructure. Fiber optics > copper+filters every day of the week.
It's vastly system dependent and also depends on who has the worst noise copper or fiber in a particular deployment. Just having fiber doesn't not mean better sound - that's a misconception. A lot of folks uses FMC to convert copper to fiber and then another FMC to convert is back to copper. Remember the Xilinx fpga used in most FMC creates a ton of noise and jitter by themselves and to top it over you have added power supply noise. All adds up but the bottom line is if you find fiber sounds better, that's what matters :-)
Having said that, I still use fiber between the Buffalo and the EdgeRouter.