You are welcome Danny
A BMW Dealer will not repair anything, they just change components at the Customers expense and no regard for cost
I would use a BMW Vin Decoder site put the Vin number in and you should get the original build sheet Look at the list of Codes S676A is the basic Hi Fi system S688A is Harmon Kardon S6F1A is Bowers & Wilkins. Then you will know the starting point and will be able to make choices on how you move forward. BMW Designers are good at hiding components in places where they can get flooded, several models over the years have had Nav/Audio in the boot buried under the floor. Plus many of those models had a boot that could become a swimming pool if a seal was damaged or failed so moving your amp out of the danger zone makes sense. As you had the 40 amp fuses melted check the speakers as well as they may have been overloaded
For service, help and knowledge there is a Register of BMW Specialists you should find more than one near you most are BMW trained they will have the equipment and Knowledge (one near me specialises in BMW/Porsche) yet is still less than half Dealer labour rates. One of those or an Audio Specialist would be on my list if I couldn't do the job myself.
Good Luck
Dave