Problem with the subwoofer [XPS L501X], maybe a misconfiguration?

Hi all, I just formatted my DELL XPS L501X and since I cannot install my driver audio from the resource disk [It marks some error, I don't know what exactly is but it doesn't unzip, I'm using windows 7 home premium] I just downaloded the realtek audio driver and the quick set driver from the dell downloads site through the dell support center.

Ok here's the thing:

I go to the waves maxxaudio control panel "pressing" the key in the quick set:

As you can see, there's no subwoofer in there like if the system had 2.0 audio [Sorry, it's in spanish] , just to be sure that my subwoofer is detected and i don't miss any driver, i try the 5.1 sound configuration, so i can see my subwoofer.

There's two things to say here, to let the subwoofer sound i have to UNCHECK the "Center" [first checkbox], otherwise it just doesn't sound, that´s the only way to make it work.

And second, when the system tests the other speakers, [the ones in the rear side] the main speakers sound like if they where another pair of it.

Obviously any media player i tried just play sound in the left and right speakers and don't use the subwoofer.

Can anyone help me with this? Could you give the first revision of the audio driver? Maybe i'm doing something wrong about the drivers.

Thanks in advance, greetings, and sorry if my english is bad i tried my best :P.

If this helps, when I'm in a skype call, sometimes skype tell's me that there's no speakers active, and when i check them, the speakers works just fine.