... I've been reading about EQ'ing headphones to 'reach the ideal'. I found a website that seems to have the measurements and subsequent recommended EQ curves for over 700 headphones. I've played about using the Fixed Band Equaliser in iTunes to apply the recommended settings, and it certainly hasn't messed up the sound, but I think I prefer the natural sound of my AKG K702 without EQ curves.
...does the site I listed above strive to EQ out the anomalies to try to get as close to neutral "as the artist intended" as possible?
That site over-corrects the headphones with unnecessarily complex EQ. And it's based on Tyll Hersten's measurements, which overall are very good, but in frequency response they are questionable. And Tyll was the first to admit that. This can make the cure worse than the disease. It reminds me of the adage: "Design with a micrometer, measure with tape, cut with an axe".
For example, 2 headphones I have listened to daily are the Sennheiser HD-600 and Audeze LCD-2 Fazor. If I apply the EQ recommended at that site, they sound worse than without EQ at all! But both of these headphones has an EQ that makes it sound better, but it's much simpler and gentler.
The HD-600 is quite neutral above 100 Hz and doesn't really need any correction. But it gradually rolls off the bass below 100 Hz. But if you EQ the low bass back up to flat it overwhelms this headphone and sounds bloated. I find the ideal correction is simple: bass boost with slope +3 dB / octave starting at 100 Hz (+3 @ 50 Hz, +6 @ 25 Hz). This restores some of the attenuated low bass yet still sounds clean.
The HD-800 benefits from a similar gentle bass boost, but I add a cut to reduce its annoying resonance at 6k that make it sound artificially bright: -6 dB @ 6 kHz, Q=2.0.
The LCD-2 Fazor is quite neutral throughout the entire range except it dips a bit too much around 4000 Hz. This is about 3/4 to 1 octave wide on each side. As with the HD-600, a single simple gentle parametric EQ works best: +3.5 dB @ 3800 Hz, Q=0.8.
The above corrections don't make these headphones completely neutral, but they reduce their deviations in a gentle way that doesn't squash the sound, making them sound a bit better / more neutral yet preserving their overall character.
Overall, here's some advice when correcting headphones (or speakers!):
1. Correct only the biggest variations; don't chase down every little nitnoid ripple in the response.
2. Use the gentlest curves and amplitudes you can. Don't try to correct it fully back to neutral; correcting it only about half way to neutral usually provides an audible improvement without overwhelming the sound.