If the aftermarket speakers caused the short(somehow) then the Moss Act doesn't cover it and they don't have to cover it under warranty. However, they also have to prove that it was the aftermarket speaker or install problem.
And you don't necessarily have to sue them, but you can likely file a complaint with the FTC as they are the ones that enforce the Moss Act. You could also contact your state Attorney General.
https://www.consumer.ftc.gov/article...ne-maintenance