My point was that the 650s sound good on their own, just the way they are.
They scale with better equipment, but you don't need expensive equipment to enjoy the 650s.
You can tweak them by removing the foam etc, but that is also not necessary.
I don't recommend Tweaks such as aftermarket cables because they have never been proven to have an audible effect and the science behind why they would have an effect is questionable. They can, however, dress up your headphones.