So... I let my ED9 burn over night with the iMore app once again for around 8 hours and that seems to have eliminated most of the airiness I felt when I used the ED9's alternative tuning nozzle. Now, with the alternative nozzle, they sound to my ears like a ZS3 with slightly wider soundstage, but I have the feeling that some of the highs are slightly more recessed than the ZS3's but I'd need to do more AB testing to confirm that.
The lows on the other hand seem somewhat muffled. I'm not sure how to describe it... I'm listening to a track with a nice drum in the background and piano with accompanying female vocalist. The piano's keys feel lively and very present. The female vocals, though very light, are somewhat recessed, more so than on the other KZ I own and the drums are there but seem to have lost all of their weight. But if I add the stock nozzle, the drums gain a new weight to them and each hit feels like a sprinkling of bass washes over the song, the vocalist's voice becomes more present and the piano retains its presence and articulation, it just sounds overall significantly better.
This is the track I'm listening to if you want to compare with your own earphones:
https://www.youtube.com/watch?v=kbMvYk4LILo
Is there any good reason to use the alternative tuning nozzle with the ED9? I haven't heard a single track yet that makes me go "oh yeah I should totally switch nozzles when I listen to this".