Just specify them in the HTML5 code like above?
What if the wav file is coming from another host? How does it send the Content-type headers?
I don't quite understand your question.
Are you saying that the html page is on one server and the wav file on another?
If that is the case, then you would put the fully qualified URL of the wav file on the other server in the code.
Note however that depending on server settings, some admins are over paranoid about things like cross-site scripting and set the permissions wrongly and it has unwanted side effects of which one is blocking what you are trying to achieve.
You can certainly try:
<source src="http://www.TheOtherServer.com/sound.wav" type="audio/wav">
Now this is where it gets interesting with mime-types and content-types.
The other server is simply feeding a resource of type wav/x-wav as specified in the mime-types section of it's config and so it's happy, the actual server which has the html code, may
need the content-type depending on how it's set up even though it's not actually feeding client with the resource.
Some browsers also require it to be present to select the right codec to play it whilst some make the decision based on the extension.
Either way it will not hurt to include it.
Welcome to the supposed standard of html.
There are plenty of these oddities, for example how different browsers handle the ACCESSKEY tag and even the ALT tag for images which are not standard on all browsers.
Firefox and Chrome also handle the new graphics capabilities of html 5 differently causing lots of mayhem and confusion.