Compared to grado SR60i, superlux HD668 gives in more clarity,wider soundstage as well as more forwarded mids (it's like the vocalist is singing besides you).No surprise about that through because HD668 was considered as studio monitor headphone.Some people will find it boring due to it's "flat" response.That is where Grado SR60i shines best in this case.With grado SR60i you will enjoy most of the song without much difficulty even with the bad recorded songs.For 668B however it will show most of song's flaws till you can't enjoy the song much anymore.

Grado SR60i produces nicer bass then 668B based from what I heard when comparing both headphones at that time.While grado SR60i can create nice rounded bass that can bring enjoyment on listening to pop songs,metals and anything that involves with drum performance, superlux HD668B produces slamming type of bass which can sound nice solely on acoustic songs.

The only thing that is similar with both headphones is that those two can be modded with better cables and pads altogether,bringing in better performance compared to their original state.