The max weight that the HTB3 speakers support is 4lbs. They fit nearly all satellite speakers so it they fall under that weight range they should be compatible.
The HTB3 speakers are designed for satellite speakers up to 4 lbs, so they would not be compatible with the Polk Audio 5 1/4'' Bookshelf Speakers. A good alternative are the Sanus Euro Speaker Foundations Stands
Products from my answer
Sanus - Euro Speaker Foundations Bookshelf Speaker Stands (Pair) - Black
I actually bought these but it doesn't look like I can use them with the Panasonic speakers. The speakers only have the small "hanging hole" in the back. If these don't work with the Panasonic speakers is there some that will?