Its been a full year since I've had the HD660S2's, time flies!
While we're on the topic of earpads, I just replaced mine with new, fresh pads. It's such a surreal experience. My original pads are compressed by 5mm in the middle, although it sucks to be throwing them out this early, it feels like a worthy sacrifice as they were used for expanding the initial headband clamping force.
I'm getting a less aggressive upper mid presence, treble feels more like a spike rather than a wide band, I
think there's less bass, mids are clearer and less resonant, and definitely a wider soundstage. It's almost like buying a new headphone without having to spend more than $50
I'm also using the foam covers this time instead of using nylon, totally new experience for sure.