Tightening binding posts problem

If they are metal, I would suggest either the AQ wrench which accepts 7/16" and 1/2", or just use a nut driver. If they are plastic, fuhggediboudit!

Pliers worked fine for me. BE GENTLE!--

I suggest some Kung Fu practice;then try again.Upgrading posts or/and using bare wire connections can be rewarding as well.The idea of using tools in this case just repels me.

GET THE MONSTER CABLE'S X-TERMINATORS!!!

X-terminators add an interface level and, while convenient, slightly veil the sound.
The AQ binding post tool is the goods - highly recommended.
If you cannot tighten them even with a socket or the AQ tool, something may be broken as Ncarv points out, or you may have to get inside the speaker to tighten the nut on the crossover side of the post - had to do that on my DSigs when I first got them.