I am looking at getting maybe a pair of Sennheiser HD497's or PX100's. Does anyone have experience using these headphones with an iPod. I guess my worry is, since that most of the mp3's that I listen to are 128kbps, are these headphones "too good" for use on an iPod. Am I going to notice the poorer sound quality even more of an mp3 versus CD audio. Any help is appreciated. Thanks.