Hi Jeremy,
Interesting what you say re HDMI interconnects. I currently use Chord “active” HDMIs. Not cheap and cheerful, not expensive, but solid and well made. Interestingly, Chord, having got out of pricier HDMIs, have introduced hybrid optical/copper wired HDMIs. Look forward to them being reviewed.
Re interconnects, I have invested in Chord Signatures. Think they are excellent (as no doubt equivalent AudioQuest ones are).
Re power supplies, I have chosen a different route, installing multiple MK K1826 WHI mains power sockets that claim to filter RFI (both ways) plus provide surge protection. In addition, I use Chord’s basic shielded power cables in anticipation of reducing locally broadcast RFI. Thinks it helps!
The Uptone Audio paper you refer to, although not specifically saying so, perhaps gives an insight to what causes “digital harshness”. Lots of food for thought.
I have definitely reduced, if not substantially eliminated, harshness in my audio only setup, but have yet to succeed in my AV system, which also suffers from muffled sound. But not sure if this mainly poor miking by the broadcasters.
Look forward to feedback on Ethernet switches (just to think about!).