Hey,

Is this your first CS-Plane? Do you use FSX-SE or the "normal" FSX?

Have you tried my suggestions in my post from Jan. 20 2015? It is important to delete all entries in the fsx.cfg corresponding to the 707. Here is an example:

[Trusted]
I:\BigGames\FlightSimX\Captain_Sim\707\cs.sound.dll.ekhatoolnlwwbcblbeeqturenzinlzwwwtlioioz=1

Just search for "707" and you will find all entries. After deleting these and reinstalling the plane the (switch)sounds should be work. This way worked for me.