Sorry it took so long to get back to you.
Filling your stands to add mass will definitely help- something like cat litter works well.
A while ago I had some Harbeth stand mount speakers and tested a variety of materials to use as "iso dots" between speaker and stand. The stands were heavy and spiked through carpet to my concrete floor. These tests included frequency response measurements as well as listening verification.
Keep in mind that the Harbeths are lossy cabinets and the speaker dots greatly affected the sound but the results are real and should apply to most stand mount speakers.
Generally speaking the softer the dot material the bass increased and with the softest material bass was bloated and peaky.
I testes materials like blu-tack, sorbothane dots, medium silicone bumpers, hard silicone bumpers, KEF LS50 acoustic dots, cork pads, etc, all sourced from amazon or hardware stores.
The worst sounding materials were the softer blu-tack and sorbothane dots. The sorbothane dots came with the stands. Bass was bloated and had noticeable peaks that were irritating,
The harder materials like the hard clear silicone bumpers gave the clearest, most clean sound. It was uncanny how clear these made the sound. They did have the weakest bass response too but if clarity is your goal use some clear hard silicone dots or rectangles.
By far the best sounding iso dot I used was the dots that came with the KEF LS50 speakers. I accidently sold them without enclosing the iso dots.
Bass was excellent, tight and non bloated or peaky. Highs were clear with excellent clarity, almost as good as the hard silicone.
Next best was the clear softer silicone dots.
See if you can order the KEF LS50 dots from a dealer- next best is medium hardness silicone dots. You can buy a bunch of them and give them a try. Very inexpensive.
Also FYI smaller thinner is better than large and thick. The best ones were approx 1/8 inch thick.
