When you install the 757 v4.6, it installs the Captain_Sim.b757.sound.GAU into the gauges folder. When you first select the 757 in FSX, after installing it, FSX will ask you if you want to RUN/DON'T RUN the gauge. If you select DON'T RUN, you will deny it's being used in FSX.


The entry in the [Trusted] section of the FSX.cfg file will look something like this (with the =-2 at the end):
J:\Flight Simulator X\GAUGES\Captain_Sim.b757.sound.GAU.acalhkquwrezrtnkehrccaokarnnanbqrciakcck=-2
and the gauge won't be used in FSX for the 757.

If you select RUN, then YES, the entry in the [Trusted] section of the FSX.cfg file will look something like this (with the =2 at the end):
J:\Flight Simulator X\GAUGES\Captain_Sim.b757.sound.GAU.acalhkquwrezrtnkehrccaokarnnanbqrciakcck=2
and the gauge will be used in FSX for the 757.

I hope this helps explain it for you.

[edit]To open the fsx.cfg, enter this line:

%AppData%\Microsoft\FSX\fsx.CFG

into the Windows Run command.
[/edit]