Comment 6 for bug 525705

I can confirm that this issue exists when the analog 5.1 (6 speaker) out + stereo in option is selected using the onboard audio on an Asus P5B Deluxe motherboard and a Creative 5.1 speaker set.

Switching to the 'analog 7.1 out + stereo in' option seems to remedy the problem (although I am not sure how it affects output as I only have a 5.1 speaker setup), as reported by Nasser. This seems to be a software issue.