I won't be quoting myself from another thread specifically geared to EQ:
Suffice it to say that a good equalizer won't introduce any important artifacts. Electri-Q in Analog mode is not a good one. Digital mode is fine.
I don't consider half an octave wide tuning narrow. (measuring at "-6 dB" point aka sqrt(2) aka half-tuning, total is about 30% wider)
EDIT: There may be issues if you don't measure finely enough where you can introduce narrow dips. This will sound "grainy" or "phasey". This is known in sfx circles as comb filtering. This and phase behavior is why you should try to simplify the eq as much as possible.
Thanks! That thread went "wheeee!" over my head. It's been a long time since I studied any sort of numerical computation.
So, I made all of my IEMs sound more or less the same, with varying degrees of "grain", thanks to the heavy EQ'ing to get a mostly flat perception. I'm backing off, and just dealing with the 7-8kHz peak, adding a bit of low bass boost, and leaving it at that. I'm letting each 'phone's character continue to shine. The resulting curves are much simpler.