I just picked up a Duo yesterday, and was a little worried about the headphone amp based on the review here. I have a pair of Sennheiser HD 380 Pro headphones, which are rated at 54 Ω, so mid-to-low impedance. I have the Duo connected to a Pro-Ject turntable with an Ortofon 2M red cartridge (MM). The headphones sound terrific plugged into the Duo, with plenty of power to spare and no perceptible difference in response than when I plug them into other adequately-powered headphone amps. So at least for me, the lack of headphone power has proven to be of no concern.