This is how I got the PFC throttle quadrant (Multi-Engine Throttle/Prop/Mixture) to work with my PMDG DC-6 in P3Dv4 in Windows 10-64, using FSUIPC (paid version).

In P3D >Options>Controls>PFC Throttle Quadrant Console> Axis Assignments>

Assign Engine 1 throttle axis and Engine 3 throttle axis to Throttle Lever 1 and 2. (Do not check REVERSE)

In FSUIPC >

Throttle Lever 1 Axis Assignment in FSUIPC

     Axis Assignment>Throttle 1 and Throttle 2> Send Direct to FSUIPC Calibration (checked).

     Joystick Calibration>No reverse Zone (checked)> Separate throttles per engine> Throttle 1>Rev (checked).

Throttle Lever 2 Axis Assignment in FSUIPC

     Axis Assignment>Throttle 3 and Throttle 4> Send Direct to FSUIPC Calibration (checked).

     Joystick Calibration>No reverse Zone (checked)> Separate throttles per engine> Throttle 2>Rev (checked).

PMDG DC-6 Options > Throttle Options>Reverse Throttle Axis>ON (Green)

The only downside for me is having to assign the Throttle Axis is P3D, and then when I am going to another aircraft going back into P3D and deleting the Throttle Axis.  I control all my throttle assignments and axis through FSUIPC. 

I’ve only used this on my system but have flown over 25 hours  using this setup.   

14 hours ago, Bluestar said:

when I am going to another aircraft going back into P3D and deleting the Throttle Axis

Why?  I have three different control configurations depending on aircraft.  Just save the configuration and then load it when you want it.  Use the Export and Import buttons, the control configuration is saved in the same location as scenarios.

1 hour ago, downscc said:

Why?  I have three different control configurations depending on aircraft.  Just save the configuration and then load it when you want it.  Use the Export and Import buttons, the control configuration is saved in the same location as scenarios.

I hadn't really thought about it, but I will give it a try. 🙂

For another method, I have 5 TQs and 5 FSUIPC.inis....

HTH

I also have multiple TQ ( and yoke and stick) but I control the assignments all in one .ini. Just assigned to aircraft type and grouped like

single piston stick

single piston yoke

single turbo yoke

twin piston yoke

twin turbo yoke

twin jet yoke

etc.

.....

and a special one for the DC-6 on my 4 engine throttle so that the revers guard lever is assigned too.