Dell 1535 5.1 sound problem

I've seen similar a similar topic at the forum but didn't work for me so I decided to open new topic.
The problem is that I can't get 5.1 sound with my dell studio 1535 laptop and logitech x-530 5.1 speakers.
The OS is windows XP pro. I installed the IDT audio drivers for windows xp. I connected the three jacks of the sound system to the inputs at my laptop as mentioned at the topic below:

http://forum.notebookreview.com/showthread.php?t=288502

But I can't get 5.1 sound.
I tried different IDT drivers but none of them worked. I selected 5.1 sound option from both the windows sound and the IDT control panel, but when I check from the IDT control panel, I can't get any sound from some of the speakers. For example the center and the rear speakers never worked (I mean with the proper connection). I'm exactly sure the speakers have no problem because I've just tried them with another system. All of the speakers work properly.

Could anyone help please? I've spent many days trying to solve this problem and there is no result at all.

 

please help me. I'm so desperate.

 

I'm willing to bet you the IDT drivers don't do 5.1 with Windows XP. I don't blame them.