Propheous is right, you can boradcast the file name or path if it is available with client application.
If there is a case where client does not have the audio file, then you can use the file Upload Service of App42 Cloud API to upload the file over the cloud. Uploading the file over the cloud provide you a URL which you can send in the message to the clients. When clients receive the URL then they can download it to use.
Let me know if it helps.