It seems that you are having some issues since you are not able to get the digital audio signal.
If you are using the SlingPlayer software, you'll need to select the "digital audio" option instead of "analog audio". This option is available on the SlingPlayer software version. If you are using the web-based application, it will recognize the S/PDIF connection automatically, therefore, you will not need to apply any modification.
Finally, keep in mind that even though the Direct TV HR24 model is not included on the supported devices list, you can use any other Direct TV IR Code, since they will work the same way.