Vista - 5.1 Sound Problem

First of all, hello to everyone.
This is my story:

I had windows xp professional and I bought my new 5.1 speakers. The speakers were powerful and were working really really good.
The problem is that I changed to Vista and I tried to install some drivers for them.
I found the driver from my motherboard's manufacturer site and I don't really know if the driver is the problem(never changed my sound card, it's the default). I change the option from Playback Devices(configure>speakers) to 5.1 and I had the 2 front, 1 center and the subwoofer working well. The 2 rear speakers are "acting" like dead. I checked the wires, I checked the settings and I even test the speakers and they sound well. But some songs sound too fade, like they are broken or something(from the rear speakers only).
In other songs they don't even act to play some music.
Another problem is that in the speakers properties (in Playback Devices again) if I don't select the speaker fill I got only front speakers working and without loudness equalization, I have to turn my speakers to full just to listen a nudge in windows live messenger

Thx for reading
Nick