It is possible, that you cable box has volume control built into it and that volume inside the cable box is turned way down. This means that the audio level coming into the receiver is really low, and you have to turn it up to compensate.
Grab your cable box remote and go into the cable menus and look for 'fixed line level out' or something of that nature. Or, turn the volume up, then don't play with the volume on your cable remote again.
This should help a lot in getting the signal up to where you expect it to be.