Don't bother amping the Meizu. Another Head-fi'er and myself have both amped the M6 and it just makes the warm sounding player rather dark. It's quite unpleasant, though I do plan to try again since I enjoy the Phase Corrected Equilizer alot. =T
But I do think they can do it in a firmware update where you can set a mode within the settings that basically switches between headphone out or line out. I'm not definite this could be done, I just don't see why it can't.
I don't see the problem of plugging the headphone output directly in your amplifier. A headphone output is just like a line-out with more power. A speaker has a low impedance and need high power, amplifier input has high impedance and need little power. Although the contrary is not true, a high power output can be used like a low power one.