What is diffuse field equalisation? I am using impulse responses from http://sound.media.mit.edu/resources/KEMAR.html

These are available as either raw or diffuse-field equalized HRTFs.

My question is: Which do I want? Raw, or diffuse-field equalized?

I am using these IRs to project single notes (generated synthetically using a ring resonator) to 12 locations around the listeners head.

π
Depends mostly on your playback headset. If it's diffuse field equalized, use the diffuse field set. For most headsets, this will be the best choice. 

The only difference is overall equalization, so you can turn one into the other with a simple filter that gets applied to all HRTFs