To follow up on this, I was able to find a working solution. In my case I connected the Laser PWM wire (on the 3-pin connector) to the Mach3 RNRmotion bord Output 1 to which I also had set the spindle in Mach3 setup.
The'-' from the same connector then connected to the controllers board +24VDC ground.
Just to make to make sure the laser would not start by mistake, I connected to the two pins from the laserboard to a NC relay that I control with an other output.
Does someone know if the above mentioned controller can understand the M11 and M10 commands?