Comment 1 for bug 114435

Okay, scratch this! It turns out that:

1) I had forgotten to turn the amplifier on for the 2nd system!
2) Despite what the manual says, these motherboards require jumpers to feed line-out to the rear socket
3) The 1st system was missing these jumpers, the 2nd had them.

I've attached photographs to my forum-post on this topic in case you need clarification.

http://ubuntuforums.org/showthread.php?p=2649266