Marc Heijligers has posted complete audio performance tests of the new iPod Classic. He says in the post “I noticed that the 6G sounds precise, crisp, but lacks 3D image and has an electronic haze to the sound. At first, this might sound like an improvement (crisp, detailed), but when listening more carefully and for longer times, it becomes fatiguing after a while. The 5G sounds less precise, but its timbre contains more harmonic information and sounds less electronic. For me, the 5G is closer to how I experience acoustic music in real life, and for me is the better sounding device overall. This is not to say that the 6G is a terribly bad sounding device! It's just less than the 5G, and sound electronic/acoustical as opposed to acoustical/musical.”
Marc did all his tests using Fuzzmeasure and concluded that it is obvious that the new audio circuit of iPod Classic is badly engineered compared to 5G iPod Video. The new iPod Classic uses a Cirrus audio chipset in place of Wolfson chipset and that can be a reason for change is sound quality. Does that mean you shouldn’t buy the new iPod Classic? It depend on two main factor one is what headphone are you using and do you have golden ear for music. If you are using the headphone that came with iPod or similar ones you won’t nothing any difference. You will notice a difference if you have a golden ear for music and you are using Shure SE530 two listen to your music.
You can read and see complete test results here: Marc Website