Regarding the op amp selection, he just used them because he had them lying around.

  "If you wanted best possible sound you'd use some actual audio op-amps rather than these cheap NE5532P. And buffer the output of the op-amps somehow. But of-course size and cost balloons if you start adding buffers and stuff."

What I like about his project how he simply used a couple magnets to hold the lid on. Microsoft did something similar on my keyboard, but I don't know that it is something used much on DIY projects like this.