I bought this to use with my Sennheiser HD-650s and my Mac Mini. It works great, the build quality is excellent, the volume buttons are very sturdy, the led lights are helpful, the audio out jack is tight.
The most important one: the audio quality is simply perfect. But to be honest, the audio out of my Mac Mini is almost that good and the Mac Mini drives the high impedance HD-650 without any problems with volume slider at 50% already loud enough to hurt me ears. The only difference I could find so far is the Groove has a bit more detail and clarity in the bass region. But I would have to listen really hard to tell the difference. In my opinion it's a bit overpriced considering it improves my Mac Mini audio output only so slightly. If you have higher impedance headphones, e.g. 600 Ohm it might be another story though. It also gets slightly hot under normal operation which I understand is not unexpected.
Apogee Groove is a nice audio interface that gives me confidence I am listening to the very best audio quality possible, however it's a bit expensive for the slight improvement it offers over high quality embedded audio as in the Apple computers. Anyway, I am giving it max score because the sound quality is absolutely perfect and that's what people would buy it for.
