Sorbothane isolation bumpers
For $17.58 I got ya covered.
These are the best thing for such, however the sliders at Lowes for hardwood wood be a quicker less effective fix worth trying.
The isolation bumpers however, are designed to disperse vibrations in the weighted bulge angle, where the sliders can transmit vibes.
The bumpers are weight specific and is identified in the product description down page.
So for these 1.25" ones rated for 15-22# ea, 8 bumpers would work, or you could go smaller and increase the number of bumpers used.
If the speaker is heavier towards the back side, those bumpers would be closer together than the front ones.
Overweighting these, cause the bulge angle to be less effective at dispersing the vibrations, as well as when underweighted.
I have used these to isolate water pumps, and you'll be amazed at the effectiveness of them. They're sort of gummy
but hold together perfectly. I would recommend a small piece of paper or thin plastic under them
as they can remove paint when lifted.