ok ive run into this problem also was all working in optical ive just pluged the 3 direct cables into the rear of the mb, windows lets me set up as 5.1 but when i test speakers i have no rears no sub and no center only left and right speaker work.... plug in optical its all good again run sound threw the hdmi and then trew the speakers 5.1 any one have any idea ive clean installed drivers etc