Leo, you are a clever and a very kind person.
You did post your complete code and I did ask for help on that code, only you answered.
For this project I could use the 24BYj's as bipolar (saving pins) and a couple of Mega's but the whole idea was to use your board, neat clean, and no drivers. IMHO chopping up your original code is a messy mistake.
That's why in #7 I asked you to please just show me the code to fill all the shift registers with the correct bits to move all steppers together to a certain position. No acceleration, or deceleration... etc.
Regards.