1. Right click on volume control.
2. Click 'Open Volume Control'
3. Go to Edit --> Preferences
4. Check off 'Surround Sound'
5. Close Preferences
6. Un-mute 'Surround Sound'
7. Plug in headphones
That should do it (worked for me on a 2nd Generation MacBook as listed above)
UPDATE: Found a workaround.
1. Right click on volume control.
2. Click 'Open Volume Control'
3. Go to Edit --> Preferences
4. Check off 'Surround Sound'
5. Close Preferences
6. Un-mute 'Surround Sound'
7. Plug in headphones
That should do it (worked for me on a 2nd Generation MacBook as listed above)