IMO it's no different than placing book shelf speakers on stands.
I'm more concerned with my wall mounted Q's than I am about the ones on the stands.
If they were out into the room it would be a different story, I would look at securing the stand to the floor.
Because of the weight of the speakers and how well they fit on the top of the stands I wouldn't be too concerned about them moving too much.
You could replace two of the bolts that secure the woofer with longer ones installed through the top plate if you really felt the need.
Edited by brwsaw (11/21/13 01:01 PM)
Towers going back on stands