I’m also planning to experiment with hempcrete and mycelium blocks in the future; unfortunately don’t have any advice right now for you.

You could 3d print a square mould with the sound dampening undulations. I’m picturing something with finger joints on the edges so you can assemble into a box with an open front, add a thrifted tv cabinet glass door on the front and some ventilation and you’re set.

Following to see how it goes. Good luck!