Does it make sense to get these if I already have HD660s?

If it’s expensive, I check BHphotoVideo first. They don’t have a huge collection, but never had an issue and their service is awesome.

I believe this is original Senn cable. Someone else can confirm.

They are out of stock now. But may be available again soon. Not 3m. Much shorter.

I have this. I also have all original 660s cables. To me, they all seem to have come from the same factory.

https://audio46.com/products/sennheiser-hd-650-hd6xx-groove-apogee-3-5mm-plug-replacement-cable-570679