I would buy a UE Impedance jack. It will help you out with all of those headphones and costs around $10. You might not notice a difference with some of them, but you might with others. It really depends on the headphones. Usually I use my DX7 attached to an o2Amp since I have really low impedance headphones (myspeakers Aeon and Oppo PM-2 and Denon D7200 and Denon AH-MM400). If I use the DX7 output I use it with an adapter and the 3.5mm UE Buffer jack.