Vista - Realtek problem with Bass management

Realtek Problem
sorry if i am in the wrong place, but i really really need help
i just got 5.1 spekers...have onboard sound device on my motherboar which is an asus m2n-mx (special edition)...everytime i install realtek and open the sound manager, it says 'asus' written on top while the same setup file when installed on my brother's lapto says realtek...the problem lies in the fact tht my rear speakers are really really soft and i can't hear them...the realtek manager does not show 'bass management' for me while it does for my brother. everytime i install it, it just shows the following 5 tabs
1. sound effect
2. mixer
3. audio i/o
4. microphone
5. 3d audio demo

i really really need bass management to make my rear speakers louder...if it is not possible then can anyone tellme where i can get another software for tht...
my driver version is 5.10.0.5672
btw...i am an xp user...