If the screw holes are stripped, you might get by with a toothpick pushed down in the hole and snapped off flush with the surface. You could also rotate the drivers if they are concentric and drill new holes.
Heavily addicted SACDBA member, starting the twelve steps tomorrow! Jay
You rotate the woofer - then get a marker and make a mark through
the woofer screw hole on the woofer, so you will know where to drill.
Take the woofer out, fill the old holes with puddy to prevent air leaks.
Then drill the new screw holes - put the woofer back in and screw it
down, be carefull not to over tighten it.