Enabling Airplay Speaker Streaming Behind a Restrictive Firewall

I like to use Airplay speaker streaming with iTunes and I know it's also possible to stream my speakers to an Airplay receiver. To do the latter I would have to disable my Firewall or find a way to add an exception in my firewall for the OSX's audio service. It's straightforward to add an exception for an application to OSX's firewall but it's not as straightforward to add an exception for a service such as OSX's audio service. Our goal is to keep our firewall restrictive and add an exception for the audio service.

This was my firewall before:

If you click the "+" button you can add Applications but it's more work to add a service that's located in a non-standard directory.

The service we want to add is coreaudiod (depending on OSX version a variety of letters can follow so in regex form coreaudio[a-z]). (source: https://plus.google.com/107604932326897342946/posts/7FgNmddTuef)

So perform a locate for coreaudio:

We want to "Allow incoming connections" for coreaudiod located at /usr/sbin/coreaudiod.

So we go back to our Firewall settings and click the "+" icon and navigate to the root. But even when we send a message to com.apple.finder to set "AppleShowAllFiles" to TRUE we don't see /usr in the root when trying to add a service to our Firewall's exception list.

The work around for this is to create an alias for /usr/sbin. Create a symbolic link using ln.

Now go back the Firewall settings and click the "+" icon. Navigate to the desktop. Click on "sbin" and add coreaudiod to the list. Insure "Allow incoming connections" is selected.