The system went out gradually. The left side then the right and finally the rear right. I figured bad stereo so I put in an aftermarket deck. Still nothing. Any ideas? there is no factory amp external to the stereo I already called Subaru. I don't want to rewire the car but if that's what it is that's what it is. Service tech suggested it might run through a body control module but that doesn't make sense for a gradual audio loss. I'll take it to best buy only because I work there and they can cover it during a shift but I just thought if I could figure it out that'd be great. The tech's there haven't exactly won my confidence.

I did just replace the front axle due to CV joint wear and the battery because of corrosion.

All other electrical components working fine?
Check continuity of speaker wires from stereo to speaker connections and check for shorts to ground on all speaker wires.
You can temporarily run external wires from the speaker outputs to external speakers, then connecting further down the circuit.