Might not even need to get a new PSU to use with the m542 drivers. The transformer says 36V on one of the secondaries, which is ideal since when rectified that will give just under 50V. It depends what rating that winding is on the transformer, but you might as well try it if you do decide to get the drivers that John S (and I) recommend. Do you have a part number / datasheet for the stepper motors this machine uses?