AKA How to make AAC/m4a stream in safari
AKA make AAC work like mp3
and so on 

To get this to work, you need access to upload files to a web server (duh!)

Put a .htaccess in the root or folder(directory) where your music is stored with these 2 lines:
AddType audio/x-m4a .m4a
AddType audio/x-mp4 .mp4

If there already is a .htaccess file, just add those 2 lines.

Note the . at the beginning of the file name.

If you are on OS X and make a file starting with a . it will be hidden from view (under default settings). i suggest calling it htaccess on your hard drive, upload it to your server then rename it via your FTP application.

Magic! AAC (.m4a) files now act like mp3s. .mp4 files are now saved to the hardrive but beats it loading as text into your safari window.

I know many people are having problems with this so I hope this helps.

I also posted this on osxaudio.com forums here