JaZZ
Headphoneus Supremus
It's by design.
FiiO players reduce the volume by 6db to allow for headroom when increasing the EQ sliders to max. This avoids clipping by the headphone amp when using the EQ, unlike some devices such as certain apple products. You want this feature. Just compensate by turning up the volume by 10-12 steps.
Alternatively you can use the cutting method of EQ by raising all the sliders to the top (which sounds the same as EQ off) and reducing the frequencies you want to hear less.
I wouldn't do and recommend this. It's true, all sliders on top sound virtually the same as in neutral position, since the 10 frequency bands of the octave equalizer have a bandwidth of roughly 1 octave. But I wouldn't rely on that – I'm sure there will be some deviations from a straight line with corresponding phase nonlinearities. This may sound like an academic objection, but what does this solution actually serve for? There's no reason to do that. If anything, it may be beneficial to only decrease frequency bands to avoid the introduction of resonances at the center frequencies. But in many cases it isn't really practical, and the benefit is questionable.
Fantastic. Thank you, didn't know of this. I'll try the cutting method since it works exactly for my needs.
Intuitively a lowering of volume by the EQ function may be perceived as a disadvantage, but it is not. If you compensate the volume accordingly, you're exactly at the same point – there's nothing lost, the digital data are fully preserved.