That "Jones on Stepping Motors" website provides lots of information. I suspect that, had you studied the entire website, i.e. had you read the entire thing rather than staring in the middle, where the microstepping information resides, you'd have gotten much less of a headache.

Microstepping is, in fact, quite confusing for one whose prior contact with steppers has been simply making them go in one direction or the other. However, if you read about the physics of steppers, and consider how bipolar stepping motor drivers work, I believe you'd have learned what you need to know.

Now, these motors you plan to use are quite small and low-torque. Much of the information available about microstepping involves high-current bridges, etc, more suited to larger applications. It's likely you could do the job with these rather small motors using an audio amplifier to level-shift and smooth your PWM.

I'd suggest you go back and read the entire piece on stepping motors. When you're finished, you'll understand them much better, including how to drive them.

RE