Games affecting my music volume (realtek HD Audio Manager)

I have onboard audio (Realtek HD Audio Manager)
mobo:asus p5q pro


My problem is that everytime i play a game, for example counter-strike source, and i have music playing in the background either from itunes or windows media player, the music volume lowers everytime there is sounds from ingame. For example, gunshots will lower the volume, any explosions i hear will lower the volume

someone said something about "smart volume management" but cannot find an option like that anywhere

thx 4 the help