I had /have the 4600 and 5400 (I think). All used the same dedication modules.

The DM stood for dedicated module, although, wierdly enough there was one called DM/S that was a standard single centre pin hot shoe, and an inlet for a Vivitar specific plug to PC plug for use with a cold shoe too.

I am pretty sure the /N2 designatio would be a second generation dedication module for Nikon cameras.

There is a selector switch on my DM/M for Minolta the shoe to tell the fals to run as manual, run with one of two settings that used the photo cell in the front of of the dedication module, one to use the off film metering of the TTL sensor system of the camera, and one to know the power output down from full manual by about 5 stops to allow the thing to keep up with a motor drive.

The on dedication module photocell guide scales were shown on the back of the flash relative to film speed to tell you the effective range and proper aperture to use.
There was a little yellow triangle symbol that gave the aperture settings and effective distances versus aperture for the motor drive mode.

I hope this information helps you figure out how to use your product.