i had a bit of trouble getting my W3s to drop down too as the back box was *just* touching the other side of the wall. I took to the bracket with some small side-cutters and *slightly* (2-3mm) rounded the bottom corner of the slots that the 'rails' on the speaker drop behind. This let them drop down a bit easier.

The plastic nuts in the w3 brackets also split, but Axiom sent me some new ones, and I put 'speednuts' on the back for good measure.