Besides the Power Button (which resulted in the Big Red Button) and the custom brackets to hold all the main components, it turned out we also had an orphan speaker which needed a home. Sure, we could have just hot-glued the speaker to the board - but #3DPrinting a custom solution seemed like much more fun. We decided to craft a 3D model of a small box to hold the little speaker.
Once we got that done on the bottom part of the case, we replicated it to make the top and cut holes in the top to let the speaker sound come through. We also added a couple of mounting parts for screws modeled after those we used on the Big Red Button.
We're quite happy with this small part of our larger project. The slots which let the sound escape are little less clean looking than we had hoped, so next time (yeah, right, I'm sure we'll do this again) we'll likely make those a bit wider and do more cleanup on them. The screw holes took one iteration to get aligned right, but once they were aligned, they worked really well. The slot on the side to allow the wires to enter the box was a good plan and don't detract from the aesthetic of the box at all. The mounting brackets for the screws also worked well.