Controlling audio signal with digital potentiometer
As long as your incoming signal does not exceed ±5.5v, you can use a digital pot like the ISL22414 that tolerates negative voltages.  To drive that, you will need a negative supply, but that can be provided easily by a low-cost voltage converter like the ICL7660 (which I have used in a product, and works fine).

Something like this:



If your signal does exceed ±5.5v, you could add a voltage divider in front of the pot.