Sorry, no this is not supported by AMS today. We do not support writing to a VOD file while streaming it.
The only support we have for write while reading is through the LiveEvent API, which requires you to be sending content into us using the RTMP or Smooth Streaming protocol. In that situation, we are actually writing fragments to storage and managing them in a format that our origin streaming servers can understand for delivery while live streaming is coming in.
If you can make your solution work with RTMP or Smooth Ingest protocol format, then you could use the Live event Pass-through mode API to achieve the desired result.
Is your question purely around audio? What is the actual use case scenario you are trying to achieve? Customer experience?