Combining HRTF with echo I am experimenting with HRTFs. 

Specifically I'm trying to create 12 impulse responses that the brain can easily differentiate.

The more distinct they are from one another the better.

So I'm trying to figure out ways of making them as distinct as possible.

My best attempt so far is to use HRIRs on the horizontal plane with varying azimuths.

I could use HRIRs for 12 equally-spaced points (i.e. azimuth 0 30 60 90 ... degrees),  but human beings can perceive tiny differences in angle directly in front (as opposed to the sides), so a more sensible spacing would be something like 0 10 20 45 90 135 160 170 180.

That's the sort of thing I'm looking into...  I give it as an example as I would be grateful for guidance in this more general enquiry, and also it shows my motivation for this question: maybe I should drop this line of enquiry as it won't help?

Anyway, I'm wondering whether HRIRs from an echoic environment may present more cues, and hence provide better localisation.

And if this is the case, is there any shortcut to actually recording the HRIRs in a cathedral (which has actually been done: http://www.ind.rwth-aachen.de/en/research/tools-downloads/aachen-impulse-response-database/)?

i.e. is it possible to take an impulse response for a cathedral,  and convolve it with each HRTF?

π
Choosing points in the horizontal plane with proper spacing seems like the right approach. Aneochic HRTFs are probably the easiest but typically lead to "inside the head" localization. Depending on your application this may or may not be a good thing. If you want externalization it's best to use binaural room impulse responses measured in a space that's similar to where the actual playback happens (there are psychological reasons for that). However these binuaral room impulse responses are a lot more complicated and require significantly more computational effort.

You cannot binauralize a measured monaural impulse response after the fact. A real binaural room impulse response consists of the direct sound plus many reflections that all come from different directions. So each part of the room impulse response contains many different anechoic HRTFs. There are however computer programs that allow you to put in a geometry, acoustic properties and then they will calculate a binaural room impulse response.