Since the audio module allows for users with permissions to upload files, I don't think Übercart has that functionality yet. (User-submitted products). But that's something we're interested in developing.

You can add any files you like to the UC "Product" content type, who the provider of the content is, is up to you. Currently it's not available for customers to upload or create their own products yet, I'm afraid. With our site we plan on offering some kind of rev-share affiliate program where customers can sign up, and create their own content; sell it on our site and receive a cut of the sales. That's not possible with UC's current status. (But again is something we - RiffTrax, not necessarily Ubercart - are looking at development early next year).

Does this help at all?