and the people who "know" how to use an equaliser may not necessarily have the same ears as you

and yes I know what an A900 is, I have one myself =P
I don't use EQ with higher end headphones like the A900, I don't think they need any adjustment to the sound. But its common for people to want a more enjoyable and fun sound they can dance to.
So an example of a midrange hump for the A900 would be:
0 0 0
+3 +8 +3 0 0 0 0
Notice how the vocals are now more lively, this is the effect of boosting the midrange. Midrange controls vocals and how much dominance they have over other aspects of your music. If you want more low end attack (more bass boom) then you would increase the frequency on the far left (60Hz). If you require more treble than adjust the settings on the far right (10-16K Hz).
Adjusting the equaliser is a matter of personal taste, how YOU like to hear your music, what YOU think is best. Not what I think or anyone else.

So experiment around, and ask yourself what aspects of audio do you like most, is it bass? treble? vocals? or everything? adjust accordingly.
Now for extra fun factor you can turn on the spatialiser, theres only one function you need from the spatialiser though, and thats the Phase Correction for the equaliser.
So Spatialiser Settings:
On
Mode: Normal
Virtual3D : Doesnt matter since mode is set to normal
P.C.E: 1 (Any more and it will shift the phase too much causing music to sound too inaccurate)
ViBE: 0
Speaker Type: Headphones
Notice how your music now sounds more vibrant and warm (more energetic you can call it). If you turn off the spatialiser you'll notice that your music has gotton dull, this is because you've gotton used to the DSP. (DSP's degrade sound quality, but make the music in general more enjoyable)
You can play around with the P.C.E setting, you may like to boost it for a more lively sound, but I suggest a setting of 1 at most. (For those using IEMs and closed headphones, I suggest turning off Spatialiser completely, the sound may seem compressed and congested if you listen with spatialiser on for a lengthy period of time)
Now, Bass boost and treble Boost:
Bass Boost: 0-5 (depending on your taste, any more than 5 will distort your music)
Treble Boost: 0
Now Bass Boost and Treble boost are a feature of the philips sound chip. I believe its part of the "LifeViBes" DSP that is programmed into the philips sound chip. (Your Meizu M6 has a philips sound chip in it in case you didnt know). You'll notice that the effects of bass boost and treble boost are different to that you can achieve using the equaliser. This is because they affect a wider frequency.
For example, bass boost in my opinion affects the entire range from 54Hz to ~80Hz and when you increase bass boost it boosts that entire region. Now with the M6's equaliser, you can only boost certain frequencies, 60 Hz and the next step up would be 150Hz. Hence using the bass boost feature of the M6 is a good idea if you like that extra rumble and "boom" in your music. Based on my preliminary analysis of the bass boost feature, it tends to start distorting music above level 3, however only ultra high end headphones/IEMs may pick that up, so in the instance of the A900 you are safe to use it up to 5, but no more (Unless you don't care for distortion, or your ears cannot hear it)
I'm pretty sure you are already accustomed to the refined treble on the A900, theres no need to boost that so leave it on 0.
Okay, once you've gotton used to equalisation and perhaps even done some research you're ready to prove me that equalisation is a detriment to audio quality.
And.. you may be right :D
As you learn more about the audio world, you will come to appreciate certain aspects of audio such as neutrality, natural sound, balanced audio, and audio quality as a whole. Its at this stage you will be using a FLAT eq (0000000000), Spatialiser off and no bass boost or treble boost. When you listen to an instrument in real life, or someone in real life, you'll realise that their voices are not equalised at all, rather they sound FLAT. Sound quality is sound that imitates reality well.
Of course, as the M6 is a digital device that is perhaps pre-equalised even at a FLAT EQ setting, do realise that your headphone is also "pre-equalised" in a way too. As good as both get, you'll never get something that sounds like reality, but.. you can try to get close. At the flat EQ setting (Not with the M6, because the base M6 output is not flat by any means), you get the most details out of your digital device, when you adjust it, you'll notice that the sound changes as well. Try listening to a song with vocals, and boost the 60Hz frequency, does their voice change? OMG it does too! :eek: now the only way you can tell if this change is for the good or not is to actually listen to that person in real life sing and see if it sounds like them.
Ok so what have i been babbling on about in the previous 2 paragraphs? I'll sum it up lol, Equalisation can make your music sound better, but in many (almost every) cases it decreases the sound quality.
Sounds Good =! Higher Sound Quality (Not usually anyway, subjective there =P )
So if you must equalise, try an advanced equalisation technique. Cut all the frequencies instead of boosting them. Cutting means, putting the equaliser frequencies below 0.
for the sample midrange hump i gave you:
0 0 0
+3 +8 +3 0 0 0 0
is an example of an EQ boost.
Now if you define a new datum, say take -8db as your new "zero"
then an equivalent midrange hump will be:
-8 -8 -8
-5 0 -5 -8 -8 -8 -8
Try this setting and tell me what you hear. You'll most likely be saying.. wait.. the music is all dark now, its not as lively as before. True. But you'll also notice that the volume has decreased quite a bit, try increasing the volume. Sounds better? If you do a comparison between EQ boost and EQ cut, and you really focus on your music then you'll hear more detail with EQ cuts. (For example, the timbre of a guitar string vibrating). The reason for using cuts instead of boosts is to minimise phase distortion. Its sort of like what I told you about setting the bass boost feature too high, you'll end up with distorted beats, its a similar case with using equalisers. The safest is using a FLAT eq, the next best thing is to use EQ cuts. (You may be wondering why flat has less distortion than cutting the EQ, that would be hard to explain, and you really don't need to know the mechanics behind audio right now =P )
and this post has gotton far too long so I'll end it there. (You'd probably have figured, my next guide [when i have the time] is a complete guide to the M6's sound enhancement features).