Control the Volume of the sound not the computer mixer, having the data C#

Question

I have managed to capture the sound from the microphone and output it to the speaker
using many ways NAudio and the Winmm.dll but the problem is that the sound's volume is low unless i get so close to the microphone then its loud !!
i have the data like this:

byte[] indata;
byte[] outdata;
Stream fiFoStream;

is there is any way that i can turn the volume up using the data bytes or i need other resources. knowing that i tried using the winmm.dll functions

string mmdll = "winmm.dll";
[DllImport(mmdll)]
public static extern int waveOutSetVolume(IntPtr hWaveOut, int dwVolume);
[DllImport(mmdll)]
public static extern int waveOutGetVolume(IntPtr hWaveOut, out int dwVolume);

and i didn't get the result needed, any help is appreciated :) Yaser.