personally i think the 681, it scoops the mid's nice smile with the extreme low and high end way up there, and for those that want it flatter with transparent mid's the 662F, no complaints on this one... strange you mentioned the 669 i think it is a very likable headphone... i think it would complement very well... if they would make it handle more SPL... I personally like the 662 better .... would like to get your input using it with metal? and the HD-668B is an all around smooth drink... just outstanding with good head... amp. i think there is a big complaint for head bangers that there is not enough headphones and ear buds designed for this music alone. now if you listened to hip hop, man you would be targeted with the most boomy unbelievable overpriced ****, that you'd have have to listen to it a second time, because you could not believe how bad it sounded the first.