asus P5b not giving 5.1 output

[ranjan2001]

Need some help I bought altec lansing VS3251 & cant get them working with asus on board sound in 5.1 channel.

It only works in 2.1 channel same was the problem with my creative speakers & I thought that since vista x64 drivers were not available from creative that might be the problem. Now the same is happening with altec speakers & I am suspecting either the mobo ports are not working or the driver is messing up. I installed the soundmax x64 bit latest v6520 driver but its not giving 5.1 sound so I googled & found this thread.
http://www.tomshardware.com/forum/21...problem-please

Reading that thread
I have disconnected the front panel audio only the rear are connected
Bios has HD sound enabled (If I chnage that to AC97 then soundmax drivers fail to load)
soundmax driver is loading too & I can configure it for 5.1 but when I press the test button I only get 2.1 sound.

Here is a diagram of mobo rear

I connected the cords as follows.
green to port 7
orange to port 4
black to port 5

only port 7 gives 2.1 sound
if I plug the black (rear speaker cord into the green port I get no sound)
i am able to only use green cord/port7 in 2.1 channel & along with that my sub woofer gives sound too without even connecting the sub woofer cord (orange cord)

For reference here is an image of the rear ports of 3251
http://www.tweaktown.com/popImg.php?img=altec_05l.JPG

Do I need a sound card for 5.1 speakers to work properly or can this be done with on board sound card.
Something is wrong but i cant figure out what?
Need help i am going crazy without proper sound even after spending for new speakers.

NOTE
I mainly need the surround speakers for music (mostly Mp3+ CDs) & will share them with Tatasky STB making a home theater. if these are not going to work which speakers should I buy.

There are dedicated home theater speakers which can work with computer using auido in/out ports from computer, should I opt for those kind, what r the advantage, I saw few at Croma electronics store.

Anyone using these speaker can you tell me how are you getting 5.1 output?

[ranjan2001]

I uninstalled the soundmax drivers, disabled the onboard card & then enabled & it asked for the driver & it downloaded automatically from MS site now I am getting 5.1 sound but a funny thing is that if I am on surround 5.1 mode the subwoofer does not give much bass output (its too week), when I press the stereo button the sound goes 2.1 with good subwoofer output.