use the presets.
an -alt preset insane is NOT equal to a cbr 320kbps with quality max and a 20500hz cutoff. nor is a alt preset exteme equal to a 128-320vbr with quality 1 and cutoff 19500hz.
there are seperate and unique algorithms for each of the alt presets that give you the best bang for your buck.
to my knowledge there are no ways to duplicate this via user deifinable options.