I have them. It's a hollow tube to allow the routing of the speaker cable. If you want to fill the tube, you might try filling a nylon stocking w/ pea gravel. But you probably would need to put the speaker cable thru first though...

I like the stands, though I wouldn't say they are dog/cat/kid proof. They will tip. I have a 2 year old girl and a crazy 80 lb lab but they're not too attracted to the speakers so it's not bad.

I'm about 80% done reconfiguring my HT so I'll post when I'm done.