What is the difference between the requirement of proof beyond a reasonable doubt and the test required by the Sixth Amendment?

"It is self-evident, we think, that the Fifth Amendment requirement of proof beyond a reasonable doubt and the Sixth Amendment requirement of a jury verdict are interrelated. It would not satisfy the Sixth Amendment to have a jury determine that the defendant is probably guilty, and then leave it up to the judge to determine ... whether he is guilty beyond a reasonable doubt. In other words, the jury verdict required by the Sixth Amendment is a jury verdict of guilty beyond a reasonable doubt." (Sullivan v. Louisiana, supra, 508 U.S. at pp. 277-278, 113 S.Ct. 2078, italics in original.)