I've got a bunch of different audio environments to play with- bathroom, concert hall, underwater, living room, stone room etc etc
Okay first off match the environment your speakers are in with the audio profile... so if you have them in a pool put the setting on underwater.

The more close you get it the crisper the sound should be.

Make sure the speakers are connected to the subwoofer if they have to(some speakers connect to both the PC and sub).

Make sure the OS (Win XP I assume) is also configured for 5.1

Otherwise you may need a sound card to get the true mileage.