Thanks maties! 

Yes, the inverse filter was constructed from the narrow band DF and ID equalization curves Tyll has for his measuring head, see the filters response vs target in previous post from august.

Anything could potentially be used as reference basis (1 or more headphones average) and I can give it a shot. In any case, it should be an average of a few positions just like your compensated response on Inner Fidelity graphs is. I can try with HD800, although the SR009 is the more neutral of the two in my biased opinion 

Also, in case you're not fully satisfied with your current eq. Curves Tyll, the suggestion I have is to simply record your own HRTF using suitable headings / headings average. You really only need a full range speaker and typical omni mic and perform the measurement in anechoic conditions (for example outside with thick foam pads on the floor).

It's then a matter of recording the speaker response at using your dummy head at target headings and the speaker response at the center of the 2 ears (dummy head is removed) such that speaker response can be excluded from the HRTF. Strictly speaking the HRTF is the L/R ears response divided by the center mic response for a given heading.

Only reason I am suggesting a proper HRTF is that it's difficult to rule any one headphone as the reference anything else should be rated against. i feel the HD800 is excellent, but has its issues with peaks in upper mids. Maybe an average of 3-4 reference headphones could get us somewhere indeed. Let me know the candidate list and I will give it a shot...