I wouldn't call them misinformed considering they've listened to both the Sundara and 660S. The 660S stands out from the rest of the 6x0 lineup as it has a good (read: wider) soundstage and decent imaging.

I haven't listened to a Sundara in a while but if my memory serves me well, I'd call the mid range on the 660 crispier (vocals sounding muted and lack of slam were the reasons I upgraded). Depending on what you listen to, I could see how someone could come to that conclusion.