It works alright with a preamp. Sounds pretty good.
If you want to plug it straight into the back of a headphone amp, you'll be reaching for the gain switch.

See the review below this one for an in-depth analysis.

The sound this thing puts out is superb.

Try to find headphones that don't suffer much alteration in an impedance mismatch, since the impedance of the MF02s is high.

Firmware updates continue apace. This means ease in loading music, and now, cover art. As seen above.