I'd be interested in comparing it with the Nothing Ear effect. If it's linear (and time invariant), it should only require playing a test sample through it, recording what happens, and using an automated script to extract the responses.

As for the effect, I was trying to get a particular effect I'd liked using earlier, rather than the most realistic spatial audio algorithm. The earwax effect mentioned elsewhere in the thread also sounds quite close to what I wanted. Posting this also worked as discovery, getting me some good suggestions for other effects to reverse engineer.