Thanks for posting in the Slingbox Answers Forum! I'm sorry to hear you are not able to get audio when connecting to your Slingbox from your TV.
If you take the HDMI cable that is connected from the OUT on your Slingbox to your TV, then connecting it directly from your DVR to your TV and are able to get the audio on the TV, that means the issue is with the HDMI out port on your Slingbox.
I would recommend trying a different HDMI cable just to verify, but if that is still not working, I would recommend contacting Sling Media Support, as you would then be eligible for a hardware replacement.
Below is a link to an aticle from our support site that explains how you can contact us:
Hope this helps!
The Sling Moderation Team