I have one of those Dave Brown mount that you mentioned. My experience is that without first drilling a through hole (of a smaller diameter than the screws), it is extremely tough to put the screw through. The mount is glass-filled and it is extremely hard. Unlike soft woods, wood screw could be easily tapped into the wood without much problem.

Now, I faced a problem, with the supplied screws with Dave Brown mounts, I couldn't get the screws to sit perfectly on the mount. I really suspect that at least one of the 4 screws does not have a good clamping force on the mount. I have tried using electric screw driver of high torque but a few attempts show that I may risk damaging the recess of the screw head, damaging the screw completely, while the screws seems stuck at the mount.

I would try a 2nd attempt to use bolt and nuts instead with a new mount of course.