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.
I still think a function programmed within the firmware would be able to switch between line out and headphone out. It goes in every "Wishlist for x.xxx.xxxxxxxxx" firmware thread by me, lol. Hopefully one day it'll actually get implemented.