Kapitan wrote on May 7^th, 2013 at 12:30am:

Hi, I wonder if anyone has altered the way volume sounds are present in the cockpit, if there is some sound.cfg somewhere. I would like to reduce the engines sound and increase wind, up to 90% or more above 250 knots, and much higher than it is now for lower speeds.

You could take a look at the sound.ini file (open it with Notepad) in the FSX\Captain_Sim\737 folder. I don't they are the sounds you need to edit though.

SO

You could open the WAV files, found in the FSX\SimObjects\Airplanes\CS_B737-200\sound folder, with a sound editing program and reduce/increase the volume that way.
Or..
Change the output volume in the sound.cfg found in the same folder as the WAV files.