Originally Posted by solidgold
Did an A-B comparison of the BMW Y-cable and standard headphone jack cable (2.5mm plug). You can hear the diff right away. Sound quality from the std headphone jack cable is just crappy. Muddled, poor bass, scratchy, blend and vocal clarity is not crisp. When I switched it to the Y-cable, the imaging is much better, clearer, better separation, improved bass, etc. Do use the same piece of music so you can compare apples to apples. So for those who only have an aux-out and find that you cannot stand the sound quality of your apple Ipad/Iphone. This is the cheapest solution.
If you plugged into the headphone jack of the iPod/iPhone, that's the issue -- it's amplified but at low levels, and is intended only for headphones. You can get a pure line level audio from the dock connector using any number of dock cables on the market (doesn't have to be BMW's). The dock line level is louder and clearer than what the headphone jack delivers, and is intended to be paired with other audio components.