Sounds like a threaded insert is used and has broken free. Best thing to do is somehow pinch the thread insert in place (so it doesn't rotate) then remove the screw. If you have cross threaded the screw and cannot pinch the thread insert firmly enough you will probably have to perform major surgery by removing the whole insert (could get ugly!). Either way you will have to somehow refasten the threaded insert, perhaps using epoxy. Without pictures it's very difficult to assess, but it sounds like proffesional help could be required to avoid mangling your speaker.
Was it worth the effort ? Advice needed...........
I purchased a Sistrum Sub Stand for my Sunfire Sub. The results were utterly astounding. I decided to put Audio Points under the bar stock legs of my Magnepan 1.6's. The removal process and installation of the points went really smooth. Upon assembly one screw from the leg mount swisted off and it will not come out. Kind of cross treaded I guess. With out any warning of a treading problem it just broke off. I put the remainder of the hardware on and set them back up. The sound difference is incredible too. But I noticed that the panel is vibrating from not being secured to the leg structure. So I'm looking for advice as to how to get this broken bolt removed. Help .........please !