How can you tell if your motherboard's audio controller is screwed up

[Blakestr]

Asus P5Q-E.... it always outputs left surround channel to subwoofer.... I've changed two sound cards and two sets of speakers....Vista 64 and Win 7.... it is the only other variable that has remained constant...I don't want to go RMA it (it has been more than 2 years will Asus still service it?)