Whats your source? If its a pc use Equalizer APO. If not then its fine to give the analog graphic eq a try, maybe even a parametric one if you can find a used one cheap. Look for used ones from like guitar center(I've picked them up for $30 shipped for dual 31band units) to keep your cost down or buy from somewhere with easy returns.could you use the ART EQ-341 Dual 15-Band 2/3 Octave Graphic EQ
between a balanced headphone dac an amp without adding any noise?
The odds of hearing an increase in noise with feedback opamp ics is pretty low, thats the whole point of that circuit design, trade feedback distortion for low harmonic distortion and signal to noise. I use current signal interconnects and if I switch to normal balanced ics I can hear putting the eq in line, but its very revealing equipment, non feedback current signal circuits on isolation transformers blah blah blah =/
Just to add I did exactly that, added an analog graphic eq in between a jds odac and o2 and couldnt hear a difference.