On the interior of the lid of the amp case, there are mounting points for both the Circuit Playground Bluefruit and STEMMA Speaker that allow for some screws to attach the boards. The mounts for the Circuit Playground Bluefruit utilize M3 sized screws and the STEMMA Speaker utilizes M2.5.
Using M3 screws, attach the Circuit Playground Bluefruit to the amp enclosure lid by lining up the holes with the front of the board facing down. Repeat the same process for the STEMMA Speaker with the front of the board again facing down.
Attach the 3x AAA battery pack to the Circuit Playground Bluefruit's JST battery connector and then close up the amp. You're ready to amplify some 8-bit tones.
The 3D printed base for the PCB allows for screws just like the Circuit Playground Bluefruit's amp enclosure. Using some M2 standoffs, twist in the standoffs into the holes on the 3D printed base. Then place the PCB over the standoffs so that the mounting holes line up and attach with some M2 screws.
The case for the perfboard version of the keyboard allows it to sit snuggly in the shallow box so that all of the electrical connections are protected and structural stability is provided. You can gently press the boards into the box and they should gently click in under the lips on the edges of the box.