I’m new to this thread, but has the OP tried experimenting with a different DAC and/or different streamer? If he was that unhappy as he describes in the initial post I am skeptical that a change in Ethernet cabling or power supply are going to solve this. His subsequent posts in the thread sound like he is trying to convince himself that each tweak has done something positive (confirmation bias).
I am assuming that prior to purchasing the PulseMini he was happy with his speakers and amplifiers. If he has been changing those while trying to improve the streamer, then he really is deep in the rabbit hole.
Finally, and I am not being snarky in suggesting this, there is the issue of his hearing. Most of us are at an age where high frequency loss is common, and if there are some idiosyncratic losses just under the highest frequencies, then that may also cause his issues.
I would start by trying to demo another streamer/DAC in his system, just to see if that solves everything