What would be prohibited by the sixth amendment

I'm pretty sure it prohibits any state from providing less protection for a right conferred by the 6th Amendment than is provided under the federal Constitution. 

The Sixth Amendment to the U.S. Constitution affords criminal defendants seven discrete personal liberties: (1) the right to a Speedy Trial; (2)the right to a public trial; (3) the right to an impartial jury; (4) the right to be informed of pending charges; (5) the right to confront and to cross-examine adverse witnesses; (6) the right to compel favorable witnesses to testify at trial through the subpoena power of the judiciary; and (7)the right to legal counsel. Ratified in 1791, the Sixth Amendment originally applied only to criminal actions brought by the federal government.

The answer is    marbury v. madison