There are several elements in EventIDE that can handle material (stimulus) lists: e.g. Renderer, Direct Sound, 3D Viewport, etc. All these element have the 'Selected Index’ property that matches the order of library items in the element’s material list. For example, Selected Index=1 for the first item, 2 to the second and so on. The order is fixed, but you can change it at design time in Material List Manager. Once the list is formed, you can copy-paste it to other elements of the same class, if needed.
If you want to keep a name of presented audio clip in the data report, I would suggest a more convenient way. If you add a proxy variable on the ‘Selected Item’ property of the Direct Sound element, it will return to you the name of the played wave clip, rather than a clip index. Thus, an audio clip can be selected by the index in code snippets, but you record its name in the data report.