Love the idea of a pachinko sound toy - there's lots of interesting physics and collision patterns to sonify. So far you're simulating those physics really well, and I think the marimba is very suitable, but when comparing your prototype to real pachinko/plinko, it doesn't have quite the same exciting speed and energy. It could be interesting to further experiment with the physics - maybe higher gravity or peg bounciness.  

I think the option to set which pegs are active is really strong as a way to shape the sound more intentionally. Almost turns it into a weird physics-based sequencer. On that note, one direction you could try if you want a more autonomous option is to have the chips wrap back to the top when they reach the bottom, so it kind of loops like a sequencer.