IIRC, being able to make an archival copy is not a law, but is part of a Supreme Court decision (i.e. 'case law'). The DMCA was enacted after the Supreme Court decision, so I would assume that legally it would 'override' it. I'm definitely not a lawyer though so I have no clue if I'm right. Either way, I'm sure there will be a case at some point challenging this discrepancy to the Supreme Court and we'll see what they say at that point.
A law by Congress cannot override a Supreme Court decision. The Supreme Court has the final say on the Constitutionality of laws in the United States via judicial review, which was used for the first time by the court in Marbury v. Madison.
