On Facebook, I just saw a hilarious video for a product called the Catacombo Sound System, a/k/a the Catacoffin. See the following link for more information.
Hmm, something tells me that we will have better things to do in the afterlife than to listen to music using the audio systems people have thoughtfully built into our coffins. But I suppose that vampires (or is that glampires) might enjoy such sound systems.
To buy something like this for one's departed loved ones is to emulate the Egyptians to some extent. They would bury (or rather, enbalm) their loved ones with all the acoutrements they believed would make for a better life in the life to come.
The great thing about the Catacoffin: Since the dead person within the coffin is highly unlikely to ever listen to the thing, blown speakers are equally unlikely. The thing will sound as good thousands of years later as it sounded on the day the coffin was buried, unless people play music through it too loudly during the funeral service.
Postscript: A guy calling himself John A comments, "If I was going to blow 30 grand on a coffin, my first priority would be an escape hatch, not a sound system." I'm with him!