hi,
to follow-up--the solution i went for was not using a de-multiplexer since the individual outputs were only addressable one at a time. instead i have two motors connected to one set of outs from the arduino so multiple sets of motors can move independently of each other. i have 10 motors instead of 12--but it is working fine for this piece.
in the future i'll try daniel's way.
thanks for the help.
-niknaz