iTunes error code (-54)

Hello everybody, I've been experiencing this issue for some months now. Unable to use the iPhone 6s for my personal music at all. Seems kinda odd considering i'm paying over $600 for a device that specializes in music and phone capabilities, but besides my annoyance with that I need help figuring out how to fix it. I have talked to a 2 different apple master technicians and a few friends that have guided me thru very thorough troubleshooting and I tell ya, there's not a whole lotta patients left. By doing research online it states this trouble code (-54) is relating to security permissions. regards of what I sync even if its unchecked for music,photos,apps,and more, and I could even try to sync one good known song and it would still give me this.