[MRtecno98]

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.

[verzali]

True, it doesn't amplify, it just focuses. So that's different to the three body problem, in which it wasn't directional as far as I remember.