I had known about the center faces being turnable for a while, and have a cube
that I have marked up so I could work on solving the center face problem. In
general, I solve the cube except for the center faces (since that was what I
already knew how to do), and then have three transforms: one that will turn
any center face 180 degrees and leave everything else unchanged, one that will
turn one center face 90 in one direction, and an adjacent center face 90 in
the other direction, and the last turns two adjacent center faces 90 in the
same direction. My transforms are rather long and rep(it)*ous.