There's no direct support for this.
You can add audio files to a slide, and the audio can be set to auto-play or play-on-click, but the audio reacts to any click on the slide, not on a specific button or object.
In this way, while you can have two sound files on the slide, you can't (easily) choose which audio track to play. By default the first audio file will play on the first click, and the second will respond to the second click, etc.. I'm guessing that's not what you want.
The easiest way to simulate this is via dummy slides, one per audio file. You can then create buttons on one slide that jump to the respective slide with the audio file in question set to auto-play. If the slides look the same then the audience won't be aware of the methodology. It can get a little messy, though, especially if you have lots of audio files that could be 'clicked' in any order.