What happens if you install it directly into P3Dv5 when installing? Or doesn't it give you the chance to change the directory of where you're installng it (as in it only recognises that P3Dv4 is NOT installed)? Sorry, but I'm not going to uninstall P3Dv4 just to test this.

I did uninstall the 737-200 Base Pack from P3Dv4, and when I reinstalled it, I was able to change the directory from E:\Prepar3D v4 to E:\Prepar3D v5, and install it directly into P3Dv5. :-/

I don't have the

<Launch.Addon>
        <Name>СS 737 Sound</Name>
        <Path>Captain_Sim\bin\cs.sound.dll</Path>
</Launch.Addon>

info in the dll.xml files found in C:\ProgramData\Lockheed Martin\Prepar3D v5\, or C:\Users\<MyUserName>\AppData\Roaming\Lockheed Martin\Prepar3D v5, but the sounds for the 737 work perfectly fine (this was after uninstalling from P3Dv4, and reinstalling it directly into P3Dv5).

After some checking, I do have this

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

info in the dll.xml file located in C:\Users\<MyUserName>\AppData\Roaming\Lockheed Martin\Prepar3D v5