Arduino mega2560 and RobotDyn dimmer module with firmata Comp tool

Hi, i have some arduino mega 2560 and many RobotDyn AC Dimmer module 8A 1 channel 5v logic dimmers.
an artist asked me to help him, but i never worked with anything out of leds, ledstrips or motors with arduino… so i’ll be really thankfull if you can illuminate me on some blackholes in my knowledge.
The dimmer module have a zc (zero-cross) pin. how to set it in the firmata COMP tool?
i’ve seen googling that a multi dimmers module use only one zc pin for all dimmers controlled by as many pwm inputs.
may i split it with a breadbord and connect all zc pins of the monochannel dimmers?
also because the arduino mega 2560 say that only pin D2 is available for zero crossing…
thanks a lot and have a nice day!
vento