The installer always adds the

<Launch.Addon>
    <Name>Captain Sim Sound</Name>
    <Disabled>False</Disabled>
    <ManualLoad>False</ManualLoad>
    <Path>Captain_Sim\bin\cs.sound.dll</Path>
</Launch.Addon>

between the the

<?xml version="1.0" encoding="Windows-1252"?>
<SimBase.Document Type="Launch" version="1,0">

and

</SimBase.Document>

lines. That includes for FSX, FSX:SE, P3Dv3, and P3Dv4 (it has been installed at least 3 times in each of these due to the original istall, and install after a PC upgrade, and installed again after a HDD replacement). I'm not sure why it didn't do it for you though. :-/