AudioStream
For more information on setup and implementation go check out the article on audio communications in the Unity section of this DevGuide.
The current solution to get and send audio to and from Icecast is to use a unity store asset called AudioStream. Note that this is not a free asset.
Here is a link to the asset: https://www.assetstore.unity3d.com/en/#!/content/65411
In order to use AudioStream, it is necessary to import FMOD into your unity project.
FMOD is available here: https://www.fmod.com/
When getting started with AudioStream, be sure to follow the readme that is included with the project as it goes over important details regarding setup.