I have to warn up-ahead that this is not an easy question to address. But hopefully some great geniuses here at Sitepoint will have the answer or at least point us toward the right solution.
We are already offering our members many services such as being able to share Photos, Videos, Polls, etc. and We are looking to offer our members PodCasting services.
And on server side only based on Php. We can accept a streaming server, if there is no pure Php HTML5 solution for streaming the Audio back. And the Audio of course needs to be super compressed as it is downloaded from client onto the server. FYI, we will keep the Audio files as files in an Audio directory and will point to them via ids via a MySQL DB.