sigmatel 9750 intel 915gm chipset

Problem description: I have a DELL Inspiron 9300 system with intel915GM chipset and integrated sigmatel 9750 sound card. During installation everything went fine. When I booted the system and worked the sound was fine with the laptop speakers. But when I plugged in the speaker jack to headphone jack there was no sound.
Solution: So I installed the Chipset driver from dell and followed it with soundcard driver from dell (both of them was for XP SP2, I ran them in compatibility mode). Now the headphone jack issue is solved.
Unsolved/new problem: I am not able to control the volume to the inbuilt subwoofer. In XP, the "open volume control" menu will list the volume of subwoofer among the other controls. But in Vista its not showing up.
My questions: Is this because of the using the XP drivers? or is this a unsolved issue? Is there a vista driver for intel 915GM chipset and SIGMATEL 9750?(so far I was not able to find one)
If anyone knows how to fix this issue kindly let me know.
-- Dilip, Industrial Controls Engineer, Birmingham, Alabama