Some of that coarse filter foam for aquariums can solve your issues. A block of this open celled foam in front of the intake keeps the coir from gumming up the works. A piece of it on the outtake disturbs the flow just enough to reduce or eliminate splashing. Another trick you can use specific to your enclosure is a wad of Java moss or a block of the filter foam in the water feature slightly above the surface placed so that the waterfall pours on to it will kill your splashes too.

Yet another trick you can employ is a bit of work with some more ledges in your waterfall to keep the water from dropping so far before hitting the surface, thus splashing.