How can I play sound through the line in port?

Hello, everyone,

Recently, I bought and restored a broken MacBook5,2 (polycarbonate 2009 model), and I would like to keep and use it. To help explain the situation, here is what has happened, what I've tried to do about it, and what I'd like to do:

- The headphones/line out jack is non-functional, and is not even detected by the Mac. Despite the rest of the computer being repaired, I can't seem to find why it physically does not work, as the connection to the logic board is there. From what I can tell, and I certainly could be wrong, the inside of the jack must be damaged for it not to register. As a last resort, I could try cleaning the inside of the jack with the power disconnected.

- I have tried using the Sound pane in System Preferences and Audio MIDI Setup to both try to aggregate an audio device and switch Line In modes on the Mac. As I could not make Output and Input switch, I downloaded the LineIn utility, with the same result. I can play through Input -> Output, such as a microphone, but I cannot play Output -> Input and simply plug my earphones into the second, working port.

- Finally, here is what I'd like to do (and I'm posting this for others that may encounter this problem on their Macs as well): I would like to play the Output (system sounds, QuickTime, etc.) from the Line In jack, and use the working port to substitute for the headphones jack.

Can this be done, or is it a theory? Or, would I need to buy a USB audio card, or load GNU/Linux and switch audio I/O to accomplish what I desire? I really would like to keep this machine, as cosmetically it's gorgeous, and run Mac OS X. I'm open to any/all suggestions--I've used Macs since 1997.

Thanks, all.