if you don't want to return the speakers, your only other choice is to re-finish them. Because I doubt the stains will go away. You can actually contact places that fix and re-finish pianos and ask them what they think.
There could have been some sort of reaction between the bubble wrap and th speaker finish that the stains you see now are below the paint
There could have been some sort of reaction between the bubble wrap and th speaker finish that the stains you see now are below the paint