For the last few days, I have been playing around with @vmax newest tweak, a 3M 7050 RFI/EMI absorbent tuning ring. I have tried a 1.5” ring on PCs and I didn’t really hear much difference. Now I use a 3” long ring and the tuning ring works!
In my system the most improvement was made on Cullen Crossover2 pc connecting to BHK Pre, the music simply flows smoother with more energy, as if the musical notes gained 10% weight (in a good way). It made a similar improvement when I switched to a Purist Audio Colossus Rev. B PC. But, when I add rings to Stealth V10, Silnote Orion M1 Ref. and Zaffino OCC Silver Dart, the effect is smaller. in fact, too many rings may not necessarily be a good thing, I played mostly the DCC Elvis gold CD (which is better than my SACD copy btw) during these tests. When adding three or more rings to the system the music became too heavy, and Elvis sounded like he had a cold. My final try was to put a 3" long ring on the AQ Dragon, here it simply made the sound worse.
My conclusion is the ring would help in tuning for sure if it is placed in the right combination of the PC and gears. Two or more rings may help or may not depend on the systems too. The best location of the ring is closer to the male connector which is consistent with finding from vmax.