I get it; you want your stereo to be louder than 100%.
You want an amplifier that goes up to 13? We can do that too! We please all kinds here.
No seriously, if you want your sound to play louder than 100%, you can open your audio file in an audio editing program like Acid or Pro Tools, max out the volume till it almost, but not quite goes into the red and export your audio file back into your game. If that doesn't help, simply go out and get some larger computer speakers
On a side note: I have noticed that my computer speakers seem to get quieter over the years. One solution I've found was to go out to the drugstore and buy an earwax removal system. Also works wonders for your stereo headphones!