Thanks for using our answers forum! I'm sorry that you are experiencing low audio issues when viewing the Slingbox through your SlingPlayers. It sounds to me that the volume on your cable box may be turned down and may be the cause here. The volume controls on the SlingRemote actually control the device you are using rather than the cable box, so that would explain why it remains low if the cable box volume is turned down.
Hope this helps!
The Sling Moderation Team