Background
I’ve been hearing the HD800S stock for a while and tonight I decided to play the EQ game with these cans once again.
First choice, as usual, is the Sonarworks profile. Just couldn’t stand it this time. 
EQ Profile of the month for the HD800S
So I went to the “build a profile from scratch” exercise. So my EQ “profile of the month” is as simple as 3 knobs – just 1 really:
Plot above means
– More sub-bass (optional and likely inaudible depending on the song): 6dB;
– More midrange: a.k.a. vocal or guitar bite. Just a slight 1.5dB boost;
– More high-treble: Ohh, air… I probably can’t hear this anyway: 5dB. 
Pre-gain
– To avoid clipping: -6dB;
– This is important when A/B’ing EQ on/off: an extra -0.5dB when EQ is engaged.
Tip of the month
Notice the orange line in the plot? It’s the phase. The more one cranks a frequency, the more out of phase the song will get at that specific frequency. There’s also a cost to that.
EQ is a tool, as just as a hammer is. 
The meme
EQ used
Stock EQ plugin from REAPER.
The closure
Cheers. 