Corsa if they make one for the Ford 6.0. If not get a Corsa muffler and have an exhaust shop build the rest.
I hate drone had a Magnaflow on an old 350 GM and it drove me nuts, I put up with it until I sold the truck.
My 07 Duramax has a Corsa cat back system the muffler is a full 4" straight through design and the best part is no drone at all, nada, none, sounds like a stock truck when riding in the cab even when pulling a decent grade under load. Has a nice jet engine whoosh when romping on it with the windows down.