The MM2001 interface IS the stepper controller, there is no separate board. It is a PIC-based 4 axis unit using a crude unipolar drive arrangement. It connects to the PC using the parallel interface. The MM2001 provides a 2000Hz timer interrupt signal back into the PC which the GMFC software uses to generate the PWM heater temperature control. The MM2001 PIC uses this to drive the heater wire and protect it against over heat - i.e. the PIC prevents the PC overdriving the heater wire in the event of an error... This is not essential, but useful, and could easily be replicated. If a non-MM2001 interface is to be used then some way to replicate the timer interrupt is needed and an example of this is here

There are optional additional interfaces MMUSB and GGC which allow a USB connection, but add no new functionality.

The parallel interface uses step/dir signals on the following pins...

Channel 1 - step = 9, dir = 2
Channel 2 - step = 7, dir = 4
Channel 3 - step = 5, dir = 6
Channel 4 - step = 3, dir = 8

Other parallel port connections:

Overall Enable from PC = 17
Heating PWM signal from PC = 16
Heating PWM feedback to PC = 11
PC/Manual mode feedback to PC = 12
Timer interrupt to PC = 10
MM2001 program mode to PC = 1

Not connected 13, 14, 15
Ground 18 - 25

So if you want to drive the TB6560 board directly a small interface board will need to be created to swap the wires around as the GMFC software has no pin configuration capability as far as I can see. This board would usefully add the components for the Timer interrupt and the heater management.

How were you proposing to control the heater wire temperature?

I suggest you start a new thread for this as it could be of wider interest and is OT on this thread.