There was a question about how to post a wav file recently and I admit, I haven't tried it, so here goes. From what I learned to day, the process is not as simple as some forums where you load right to the message. You need to upload a file and then take the embed code that appears as a result of the upload and paste the embed code into your message.
Right after encoding the codec doesn't seem to know what to do about anamorphic 16:9 video and BOY, it takes a LONG time to code. The embed code isn't the easiest to find after a long encode, but I have inserted it above. I'll try an audio file as well to see if the process is the same....And I see it now reads the anamorphic video, but runs the video and text off the edge of the page. AH, but that's just in preview mode. Once you post for real the text and picture display properly! Cool!
OK, much shorter for audio, smaller file: 4482_amanaftermyownheart1.mp3.zip I grabbed the code and went back to the original posting window and pasted the above code in. You can download it, but not play it from within the Cow window. So I guess you could make a blank movie with the audio file so you could play it within the Cow window.