Unfortunately amatrix isn't integrated into Maxima at all;
you'll have to call new2old_matrix and do any other transmogrification
by hand. For example, plotting functions probably expect lists,
so you'll have to extract the rows from a matrix or something.
Sorry that it's so messy.
If you just need to load some data and make plots, maybe R or octave
would be useful to you.
HTH, Robert Dodier