This sound system is definitely DIY: be prepared for some light crimping work and to pin connectors and install a speed sensor on the front axle.
For the Zero, mind the size of the speakers; the smaller speaker pair are easier to mount than the single large speaker, unless you have the OEM crash bars.
Preparing a custom sound file involves using a simple utility to process it for the embedded computer. Prior to that, you'll want to use an audio-processing tool like Audacity to fit your sample into its requirements.