Arduino 6 Axis Controller

I m looking for a 6-Axis controller, For a CNC application.

I had come across Arduino Due + G2 core firmware which can handle this. The Arduino Due development has stopped/ It has retired.

Is there any alternative to this?
Like a firmware for Arduino Mega2560 which has enough ports to run a 6-Axis. Preferably Gcode Interpreter like GRBL.

GRBL firware is available but can run 4 axis max on Arduino Mega.
Is there GRBL firmware to run 6 Axis?