I think it also takes some extended listening, over weeks or even a few months, to really appreciate what the 660s does better than the 650. Surface level I could see many people preferring the 650, but over many listening sessions you start to get the sense that the 660s just has more detail and is bringing more out of the recording than the 650. Its difficult for me to explain, but to give an analogy it just feels like I'm switching to a slightly worse prescription of lenses when I switch from the 660s back to the 6xx, like stuff is ever so slightly out of focus or blurry around the edges. In reality they are both amazing and quite close, but the 660s is just better overall and I think it takes a while for that to really show.