Hi,
that controller board has three stepper drivers on it. If you remove the controller you in effect remove the stepper drivers as well.
The six white ICs on the board look like optocouplers to the driver ICs so it might be possible to 'insert' signals from another controller and have the drivers respond to it and
leave the existing board in place but the controller section of it would be idle.
While you could do that unless you have fair electronic skills it likely to be a battle. I note that you said the power supply is 24V. That is a low voltage for steppers
and they will be pretty slow. The golden rule is that with steppers the higher the DC input voltage the faster you can spin them without stalling or missing steps.
Given the comparatively low voltage which could be a reflection of the voltage limits of the driver ICs then the effort to modify what you have just to use three
underperforming stepper drives becomes even less attractive.
It is highly likely that you will replace the stepper drives at some point. Those driver IC's are pretty tender. If one blows you have to desolder it and replace it.
If you cant desolder without damage to the board or you can't find/buy a new IC then you throw the whole board away. Even if the ICs didn't fail you will be
disappointed at the axis speeds you can achieve with only 24V.
The real option is to replace the controller with a Mach4 ready board, fit a breakout board should your selected controller require it, and replace those stepper drivers
ideally with a matching high (50-70V) voltage supply.
Clearly if you are buying quality parts the you may expect to spend $500-$1000. Is this within your budget? The fact that you have bought Mach4 means that you are committed
to getting a Mach4 controller, the simplest and cheapest from known manufacturers are $120. Such simple devices have 'one ports worth' of IO. They are adequate for
a simple router but lack the IO for any real expansion. The PMDX-424 has two ports, the ESS has three ports, the UC300 has five ports and the 57CNC has the equivalent
of three and bit ports. Any of these devices will work, all have reputable backup.
As for stepper drivers Gecko has a well deserved reputation for quality and reliability. The G540 is a breakout board and 4 axis driver combined. It is 50V capable,
good but not earth shattering. Many people use it with satisfaction, they are $300. You could also buy individual Gecko drives which are rated to 70-80V but
they will cost something like $150 each
A number of experienced CNCers on the forum recommend Leadshine AM882 drivers, capable to 80V and up to 8A. They can be had for about $80 each, good value.
Craig