iPod Touch 3rd generation specs

I would like to know the audio line out (headphone jack) output power and impedance spec for the 3rd generation iPod Touch. I am using different headphones (not just earbuds) and I would like to know this in order to get the best performing and most efficient headphones to use with the iPod Touch. I also use these with my Macbook. I could not find this spec for either product.