Nothing worked as well as the Herbie’s Audio Labs threaded Decoupling Gliders on the stand.
My experience, too. I recently installed Herbie’s giant threaded gliders under my four-post Sound Anchor stands for PMC IB2i, which are 95 lb monitors. I’m extremely happy with the results. My flooring is engineered hardwood glued to the slab. I previously spiked directly to the slab (before the hardwood was installed), then spiked into Herbie’s titanium glider cups. His glider cups were far and away better than any other cup I tried, including the ones from Sound Anchor. The big threaded gliders are better yet--and much better than the small threaded gliders, which I also tried, at least for my application.
By far the biggest insight: the height of the woofers from the floor has an astonishing impact on bass clarity, and hence everything up the chain through the mids and highs. I mean very, very small adjustments--a half-turn of each threaded footer, or less--altered the sound, once everything else was set in placement and the speakers were perfectly level. Get that woofer just a touch too low and the midbass thickens; get it just a touch too high and the bottom thins out. Surprised the s**t out of me! Woofer/floor interaction is little discussed but man, it’s important. The Herbie’s are threaded all the way to their low-profile base, so you can really dial in the height.
The IsoAcoustics were on my radar, and I even had the option to audition with return privileges, but they would have raised the woofer up too high, so I passed. No doubt they are excellent in the right situation, however.