Yes, it will make a difference. A common result is tighter bass and better focus. I bought a bag of playbox sand from Home Depot. There are other materials that are recommended, but this is inexpensive. If you use sand, you should probably fill them outside, as there will be quite a bit of dust created.
How are the stands coupled to the floor? Spikes?
jd
How are the stands coupled to the floor? Spikes?
jd