I am having the same problem. I have tried dozens of configurations for connecting pass-through. I believe I have complied with all of the suggested parameter adjustments. Finally through Mission Planner I was able to connect to the ESC and update its firmware, but it seems to have only worked for ESC#1. I needed to turn off Low RPM protect to get the low KV motors to run. It worked, but only for the one motor. I cannot get the BLheli Suite32 188.8.131.52 to show all 4 ESCs of the 4in1. I have all of the ESCs on the AUX outputs and the servo functions transferred to them. This has tied up the effort for days. I first wired in a Typhoon32 4in1 ESC, then replaced it with the Bardwell 4in1 which seems to have the same problem, so I am sure it is some configuration issue. The Cube is running Arducopter 184.108.40.206 I have lost count of all of the videos, tutorials and documents I have consumed. Is this a lost cause? Why is there so much confusion and conflicting documentation?
Tarot Ironman 650 Quad X airframe with extended motor mounts (actual wheelbase = 775mm)
Pixhawk 2.1 Cube with Here2 GPS
Frsky 8XR RC and Frsky QX7 TX
915MHz Telemetry to either Mission Planner or Q Ground Control
Bardwell 4in1 BLheli32 ESC
MultiStar Elite3508 268KV motors
6s4p Li-ion Battery