well i cant actually say that they are better than the icon 3's because ive never used those icons but compared to icon 2's, there's no comparison. cassettes are so much better on so many different levels.
they have jacks on the ear pieces that prevent from ripped cords because they fall out if they get snagged on anything. (very glad that they have these because i had an incident just this morning where the caught on a cabinet and they fell out saving me from buying new headphones.) the other plus is that the side extenders to fit everyone's head are made of metal, not plastic witch seem to be my most hated thing with the icons. they break very easy and these new cassettes with metal will probably be difficult to break. i recommend you buy the cassettes before you buy the icon 2's but if the icons havent changed durability wise, the cassettes are they way to go!