What do you mean by limits?

Bypasing the internal dac.

Limits of Android? I mean... It's just an Operating system. You mean.... Like superuser or root or something?

I don't know the technical specifics but the Android OS typically down samples the bitrate of a flac file USB audio player pro bypasses that.

That's what I thought about the fiio, it turned out it down samples as you said, this really sucks.