I am using this connected to the Topping D50s DAC. It drives my AKG K712 and Sennheiser HD headphones. It can drive them both at the same time which I especially like because now both my wife and I can listen to the music at the same time :-) or I can switch the headphones for different genres. And it sounds fair enough good. Clean, no hissing or buzzing, not warm sounding, not cold sounding, the bass is good, feels like it has a tons of power, around 10-11 O'clock on high gain sounds like you are at some live concert. I also like the way it controls it's line out so when you turn it on it disconnects the line out (to my amp+speakers). The relays operate quietly and quickly. The volume knob is smooth. The device feels robust and really nice built. Tried also some other opamps but eventually returned to the original LM49720. So here is a first con: there is simply no place for some custom built opamps on adapters, only for regular size DIP8 chips. Keep this in mind if you want to give a go to some opamp rolling. The only real big thing I could image that would make this device just perfect would probably be a remote control as the volume is already digitized. But, well, for the price, it already has many qualities and features. And perhaps the biggest and serious con is a power button that serves as a power button on long press and as a gain switch on short press. So the one has to be extra careful when operate this button and listening at low gain because a short click will switch the output power to high gain.