The Meowsic cat piano is amazing, but a bit too quiet. I knew I had to give it a line out so it could be heard meow-meow-meowing far and wide, and enhance the sounds with guitar effects pedals!
This mod is based on the circuit found here, with some adjustments to parts and techniques.
Don't have a Meowsic Cat Piano? That's OK, this can also be a helpful guide for anyone wanting to add a line out to other sound toys.