I found the HD660S to be a great improvement over the HD650 for my tastes, with a much wider soundstage, better clarity & energy overall

The HD660S sounds great on every source I've tried so far, but it truly shines with my Modi Multibit DAC & Magni 3 amp stack

With a size 7 5/8th" head, the HD660s were super comfortable to wear for long periods of time.

The HD660s are very accurate and can bring out flaws in lower quality sources

The HD 660 S is incredible