Know more about this : http://www.togeo.com/togeo/wordpress/?p=38

If this is your case it can be solved by cabling from the audio-out to line-in.

Learn about this solution : http://www.directproaudio.com/product.cfm?directid=53184

Even if the line is installed 1AVCenter might pick up an audio line that isn't in fact the correct one and in this case you'll have to change the audio line yourself using the 'Profile Capture Settings'.

There you'll see all listed audio lines that you can then change and verify which one works.