Howdy Brown Tom,
It's unfortunate that you are having issues with the audio quality on the Slingbox. There are numerous reasons as to why you are receiving poor audio quality. There could be bad audio cables, ports could be going bad etc. Before we can determine what the issue, some troubleshooting needs to be done.
1. Change the audio cables connected from the set top box to the Slingbox.
2. Connect the audio cables from the set top box to the TV directly to check the audio quality.
3. If you have the option, optimize your audio inside the set top box settings itself.
If at any point you receive audio, I suggest to not continue with the other steps.
Hope this helps,
Sling Media Moderation Team