When does it start to clip? I have the HTC Butterfly s and the overall audio quality is very good. However, using 16 ohm IEMs at 12/15 of the volume, it starts clipping with bassy notes. During Android 4.2 it was an awful crackle that was very obvious, but after the 4.3 update it's a more subtle pop. With my Panasonic HTX7 (40 ohm) it only starts to crackle slightly at 14/15. On my iPad 2, I noticed a similar crackle but it is only present at the maximum volume with IEMs (which is still a lot louder than any smartphone I've heard). I think HTC had some problems with its headphone amps as some other people also reported the same problem. Using PowerAMP with limiter and DVC resolves this problem but introduces occasional "popping" (similar to audio skip on older phones), so I just got used to listening to music at lower volumes with the stock player. I assume the stock player uses a different audio thread so it doesn't skip as easily, but there's no way of using a third-party equalizer with it.
Does a third-party equalizer work for the M8's stock player?
Take a listen to the slow breakdown of Touch by Daft Punk and see if it crackles. Of course, the M8 uses a new DAC but crackling or clipping is not uncommon on Android devices at high volumes, as well as hissing.