Is it MetaCortech or MetaCortex?

   It's both, according to the first movie.  It's spelled "Metacortex" outside the building (just as it is in MxO), but a sign that we briefly see while Neo is trying to escape from the Agents says "Meta Cortechs".  It's not MxO's fault.  PoN is just pulling a nice bit of continuity there. ^_~