Surround monitoring issue

Hi

I have a ASUS P5P43TD PRO mainboard which has 8 channels Audio output and I plugged a five speakers set to the mainboard audio outputs and set the configuration on Realtec options to 5.1 speakers mode.

Then there's no additional audio channel mapping both on Audition And Premiere for surround monitoring, there's only 2 channels appears on channel mapping.

Please help me to find out there's a software problem or hardware issue.

thanx.