It wouldn't amplify them, there's no energy gain. A gravitational lenses just bends the trajectory of the waves. If you do it right it may be possible to use th

It wouldn't amplify them, there's no energy gain. A gravitational lenses just bends the trajectory of the waves. If you do it right it may be possible to use that to focus the signal on a directional trajectory(as in, the same energy is redirected in a single direction instead of being spread out), if I'm not mistaken.