Failed to link AUX passthrough to FMU PWM OUT port of PIXHAWK 4

Hi there,

I tried to use RC passthrough set up for FMU PWM OUT(AUX port-2) , but failed.
the autopilot is from holybro, pixhawk 4.
the version of px4 software is 1.12.0dev.
the airframe is Generic Quadcopter x

A. in radio setup of QGroundControl, i assign AUX2 passthrough RC channel to channel 6.
B. in my remote controller, i assign a button to channel 6.
C. my 4 configuration files is as follows:

1)ROMFS/px4fmu_common/init.d/airframes/4001_quad_x:

. ${R}etc/init.d/rc.mc_defaults
set MIXER quad_x
set PWM_OUT 123456

2)ROMFS/px4fmu_common/init.d/rc.mc_defaults:

set MIXER_AUX pass
set PWM_AUX_OUT 1234

3)ROMFS/px4fmu_common/mixers/quad_x.main.mix:

R: 4x
AUX1 Passthrough
M: 1
S: 3 5 10000 10000 0 -10000 10000
AUX2 Passthrough
M: 1
S: 3 6 10000 10000 0 -10000 10000
Z:
Z:

4)ROMFS/px4fmu_common/mixers/pass.aux.mix:

M: 1
S: 3 5 10000 10000 0 -10000 10000
M: 1
S: 3 6 10000 10000 0 -10000 10000
M: 1
S: 3 7 10000 10000 0 -10000 10000
M: 1
S: 3 4 10000 10000 0 -10000 10000

D. first ARMed the vehicle, then, I switched the button of my RC back and forth, and test the output of AUX-2 port(FMU PWM OUT). There are NO responses !!!

E. By the way, the MAIN - 6 port is good.

Anything wrong ? Please give me a help. Thank you very much.