The HD650 are breaking in nicely and I find them very enjoyable.
A bit stronger foundation for the bass notes compared to the HD600, similar warmish and sexy mids, smooth and easy on the ears upper mids and highs. Hard not to fall in love with such easy going, relaxed and musical set. Comfortable, not heavy on the head, smooth sounding, rather forgiving and more tolerant of less than perfect recordings. I find the pairing of Asgard 2 and HD650 very enjoyable for extended listening sessions.