Check out one of the "use a PC power supply as a lab power supply" there is much good information there...
Just do a google search. Since the M4-ATX is essentially a PC power supply designed to run off automotive 12volts you should be able to follow most of the information given.
Also note that people have had issues with noise with the M4-ATX power supply. You MAY be better off with a different power supply designed to just output a set voltage. But I would check out the links telling you how to make a PC supply into a lab supply and you should be set.