I recently bought similar stands for my HT system. They wobble a bit. That's not important to me for HT but would be more of a problem for a music system. I recommend a cheap metal stand that you can fill with lead shot. I have those for my speaker system and they are very solid. Of course, each one is filled with 25 lbs of lead shot.
BTW, if you decide to fill with sand, be sure that it is clean sand (i.e. no beach sand, etc.) or you will have new and, uh, interesting odors in your house.