I would not bet too fast or too much money on the discountinuation of the HD650 or even of the HD600. It would make sense for Sennheiser to keep all three models if the demand from customers justifies it. This new HD660 seems like a lower impedance version of the HD650. Some will happen to prefer it, some will continue to prefer the HD650 or the HD600, which each having distinct sound tuning, although sharing close similarities. The are a few HD500 series headphones... in the same way if demand justifies it there is room for three HD600 series models (and i’m not even counting the closed back HD630 which is a totally different concept, sharing none of the caracteristics of the HD600/650/6xx/660 models).