Personally, I take GSMarena with a grain of salt, but FWIW...
The HTC One (M8) audio quality is by far the best we've seen a mobile device produce so far - and that's including tablets. Even its impressive predecessor pales in comparison with the latest HTC flagship, which is not only the loudest around, but also delivers perfectly clean output.
The HTC One (M8) did perfectly in the active external amplifier part of the test, posting great scores all over the field. In addition it had volume levels higher than every other mobile device on the market right now.
More impressively, there's virtually no degradation when you plug in a pair of headphones. The stereo crosstalk rises so little that it remains better than what some smartphones deliver without headphones. The rest of the readings remain perfect too, while the volume is as high as they come. What do you know - dropping the Beats logo actually led to even more spectacular performance by the HTC flagship.
Notably, they did not show iPhone in the comparison.
Edited by Baroninkjet - 3/25/14 at 1:20pm