I can't guarantee this will solve your issue, but I was getting a video stream with no audio and this is how I fixed it.
Problem started when I switched from using the analog audio outputs to S/PDIF digital. Sound was passing through for at-home watching, but Slingbox player was mute. For some reason, Slingbox has removed the audio configuration options for their web set-up tool, so I had to download a legacy version of the SlingPlayer to my system. Click on the "downloads button" in the navigation above and look for the link in the sidebar. It's available for Windows or Mac.
You'll have to go through the configuration process, but you'll have the option of configuring the audio. Select S/PDIF digital from the options and the sound should immediately start streaming.