Hardware in the loop (HITL) with external 6DOF

I have a system with the following configuration : Fixed wing with orange cube running ardupilot FW and mission planner as the GCS.

I have a 6DOF simulation which I would like to integrate and run with the orange cube and the ardupilot.

As I saw in the ardupilot documentation - the current versions of the ardupilot do not longer support the HITL configuration.

Can anyone point me to a guide or any documentation that enables a workaround ?