[eaglezsoar]

Mark, that power supply is rated as a 7.3 amp 48V switching type. Are you sure that 7.3 amps is adequate for your application?
I try to avoid the switching type supplies, there is just too many parts that can fail. There are a lot of the switching type supplies running
CNC; I doubt that back EMF destroyed your power supply. You indicate that all worked fine until your motors were placed under load
by being attached to the lead screws, this seems to point to inadequate current either by the power supply being defective or the output is too small.
Bipolar Series gives very good low speed torque. But because of the high inductance, the torque drops off rapidly.
Bipolar Parallel gives good low speed performance and its low inductance allows the torque to be held out to high speeds. But we need to increase
current by 40% to get those advantages. Changing to unipolar would require new drivers and I see no advantages to do that.
Using your 24V power supply may be a simple way to see if your other supply is defective. Now I know why I like the humble toroid transformer and rectifier, there
are less parts which means less problems but you must size any supply for an output that is more than what is needed, simply because you need a little overhead.
Best to you Mark and great job on assembling the machine with such a nice paint job.
Regards,
Carl