I've had the uDAC for a few days now and it can definitely handle its own as a headphone amplifier with my low impedance
a900's. The increase in transparency from the uDAC compared with just using the EF2's usb DAC is very noticeable, especially with classical music or male voices. However, I still prefer the added warmth to the midrange by feeding rca's to the EF2 from the uDAC. For $99 ...