FiiO L9 L-Shaped Line Out Dock (LOD) Cable For iPod and iPhone
I am using this cable with the FIIO 6 amp and it made a huge difference in volume and sound quality. Would deffinitly get one of these if you have a headphone amp or plugging into your aux port in your car. Although, you may want to get a different model LOD like the L3 if you are using it for you car.