LED screen info - BleepLabs/Arduino-Light-And-Sound GitHub Wiki
Any of the 8x8 addressable LED screen you see online will most probably work just the same. WS2812, WS2812B and SK6812 are pretty much clones.
I soldered 470uF capacitors between the 5V and ground connections on the LED board to reduce noise. Without them the audio output is definitely more buzzy.
The diffuser is made of this special plastic which is designed for this purpose. You can order it precut for a very reasonable price. I just drilled the holes in it and cut some MDF to make the mount. The screen is mounted to the black MDF piece with foam tape.
The reason the screws are long on it is so you can set the LEDs back from the screen to adjust how diffused you'd like the individual pixels to be.