I had them, sold them. Personal opinion, HD600 is better. Clearer sounding, more sparkly and more balanced. HD660S sounds too muddy, goo-y, like you're in a square room with walls covered in sound deadening material. Maybe in purely vocal tracks HD660S could better but I preferred HD600 as it's a more versatile headphone.

Apple M1 is 5nm.

I suppose it's a chicken and an egg case, but will that be enough time to give countries to build out a whole infrastructure to support charging? Maybe some super battery will get invented by then, but so far it's just sci-fi.