I have always found the argument of 'true audiophiles' that EQ or any form of tone controls on Hi-Fi equipment as mis-informed nonsence, and generally a fairly snobbish approach to audio. This was directly in reference to HiFi rather than headphones etc, as the simple fact that no Hi-Fi or speaker can produce a perfectly flat response at all listening levels in all rooms, and as a professional sound engineer of many years, I have spent time setting up system, using many methods including serious measuring methods, using frequency, phase and time. I can tell you catagorically that a room has a massive effect on sound, and even temperature and humidity make a huge difference. I could go on more, but I will try and keep this relatively brief.
Now, I am not condoning huge amounts of EQ, as EQ has a huge effect on the phase of the sound, which can and will interfere with the way it holds together as a coherant source, but I do believe that some sensible EQ is usefull, like basic tone controls on a Hi-Fi setup, so that at low levels the low end can be boosted etc, or in a very reflective room the highs can be tamed. Obviously full parametric is what professionals use, but to try and incorporate it into domestic systems would be expensive and a lot of people would not know how to use it properly, but in the right hands it is a hugely powerful tool.
Also, having listened to some high end systems like a top of the line Linn system, I thought it sounded awful - too aggressive and with no real low end, mids that jumped out at you and high's that were simply brash with no real sparkle. Having worked in studios and live environments a lot, I don't believe this is what is produced in a studio, as studio monitors are usually very neutral but with much more extension in the low end, and incredibly open and sparkly top end.
Anyway, I have wandered off the point a little, so back to players and IEMS......
The big difference here is that there is no room effect with headphones, so I believe this is a lot different to hi-fi, and I am no expert with this regard. I feel that a good player/amp/headphone/IEM combination should sound pretty much great flat, and the componants should be purchased to suit individual requirements, but then it comes down to pure preference. For example, I like my low end, preferably the lower the better as having spent many years with large PA system, you kind of get used to serious sub bass, and it is quite addictive! So, for me, I have my iPod with a line out cable feeding into a FiiO E7, with my Triple Fi 10's and custom tips and I have the EQ setting (bass boost) on 2. Now i know that's probably not a reference signal, but it makes me happy, and that for me is the key - I am happy. With my personal setup, I am the only one listening to it, nobody else can hear it, so I will do what it takes to make me happy. When I am setting up a PA system I will attempt to set it up with a flat response and try and make everyone happy.
So, IMO do whatever you need to do to make yourself happy and who cares what other think!