Less pressure will give you less velocity and thus less splash, but also less distance (just getting a lower GPH pump or restricting yours somehow like by kinking the line). Having it land on an object that dissipates the sound will be tricky, that's flow dynamics and engineering level stuff, way beyond me. I do know that a weir's shape changes the velocity and speed of water, so it's possible you can design it, but I haven't a clue where to start with the shape you'd need. I think GGBUD's suggestion of trying a triangle (pyramid shape, or perhaps a cone) is as good a place to start as any (especially if you have a 3d printer and time to kill), but so might be Lisak1's pebbles idea. I think you just have to try a bunch of things and see what works. I'll throw in one: try having it land in a mat of cat grass grown in a fodder style (no soil). Growing fodder (you can use whole oats, whole wheat, whole barley, or any other grassy grain):