Floor Resonance and Full Range Speaker Stands

If there is any way to bolster the floor with some additional lumber & floor jacks underneath the speaker locations, I believe that would provide a better solution than basic speaker stands which likely will couple additional energy into the floor perhaps shaking it even moreso?

I isolated my Dunlavy SC-Vs from the regular joists and then supported that section of floor to the concrete below. This was a huge improvement, easily measured with a real time analyzer. Floor jacks are a cheap experiment

Supporting the floor from below is the best way to go, but if it's on the second floor or some location where that is impossible there is an alternative. Get large slabs of granite. The bigger the better. These will not move much, and will distribute the energy to a large enough area that it will not cause the floor to vibrate as much. You could even try to put some sort of absorber between the granite and the floor (such as a dense piece of carpet), but due to the weight of the granite that might not help much. As to where to get granite--well you can go to the kitchen counter place, but that's going to probably be pretty expensive. It's better to try the guy that makes tombstones and mispelled someone's name one day--that piece of granite will be pretty cheap.