Ok,
Let us be clear. Content plugins are not processed when displaying quiz questions. The only way for now to embed audio is to use "embed media" button or something similar - if it is supported by you WYSIWYG editor. As it is described for some editor in the link we suggested you:
www.astahost.com/info.php/how-embed-swf-files-joomla_t10713.html: "Try going to Add New Content. Then, in the WYSIWYG editor, there is a Flash button (represented by te Flash .swf file icon), click on it and follow the steps from that. I think you will need to upload your .swf file first and then provide the external link to it." This describes how you can add sudio in swf format.
We are going to add ability to process question content with plugins in next couple of days.
Regards,
ARI Soft