Simulating protein with chromophore using amber forcefield

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Hello, I would like to prepare a system that contains protein with a chromophore and simulate using amber forcefield, all in gromacs. The system can be easily prepared using CHARMM-GUI if I chose to simulate with charmm, but not with amber forcefield. While this can be achieved using ambertools (Cookie Absent, Amber Basic Tutorials - Tutorial A26), it seems like same thing can also be done in gromacs (according to the JCP paper). Is there anyone aware of this?