If that theme component, or the existing Discourse Soundcloud onebox doesn’t meet the requirements, Soundcloud has an API and a Javascript API wrapper that looks interesting: API - Guide - SoundCloud Developers. I don’t think requests to get or play public tracks require authentication, so it should be possible to use the API in a theme component. The Discourse site owner would need to register an app on Soundcloud to generate a client id.
I’m interested in this, but probably won’t have time to create a Soundcloud theme component in the near future, so I’m just leaving this information for others.