Gobble,
I'd get all your hifi "listening" equipment off ANY kind of glass, tempered or not, in an absolute hurry. Glass is the worst sounding thing you can put audio equipment on as it rings with horrible resonant frequencies directly in the listening frequency range.
Try wood and other materials, but please do try and stay away from glass if possible.
EDIT: Also, if your speaker stands allow it, fill them up with sand. Pack it in well so that you get the maximum amount of sand in them. Then spike the stand into the ground and finally spike the speakers into the stand. Let me know if you're able to do that and report back on the sound you are hearing. PLEASE GET EVERYTHING OFF ANY KIND OF GLASS
I just don't want you to mess up your listening experience as glass is just horrible horrible horrible. Don't know why the hec they use it for audio equipment stands. Such nonsense!
EDIT 2: The sand filled stands provide a secondary earth for vibrations to dissipate from and into. Vibrations from the ground won't get into the speakers and vibrations from the speakers will drain into the stand.