I have to update my thoughts on the 3.Ai a bit. I had them up for sale last week as I felt they were a bit too bright for me. I don't think they would be for most others, but I am sensitive to treble. Yesterday, I used these on and off along with my SE215 and HJE900 during about 24 hours worth of flying. I ended up having the most enjoyable listening experience overall with the 3.Ai. Again, I am using foam tips and they make the 3.Ai much more tamed up top in my opinion. That works great for me and made them much easier on my ears for long periods of time. The SE215 was still the winner in terms of fatigue resistance and I used it for the longest periods of time as a result, but the 3.Ai was a nice reprise from the rolled-off treble of the SE215 from time to time.
I also found that I wasn't yearning for more midrange in the Heir. It never felt recessed to me before, but there was something I didn't love about it. Maybe my mood changed or something, but it seemed just right for my flight and while waiting to clear customs in Saudi for THREE HOURS I also got the chance to audition the SE535 and Westone W4 in the Atlanta Airport. I would have loved to spend more time with each, but first impression is that the SE535 is way mid-forward... The W4 was very nice in just about every way. It seemed quite balanced to my ears in the best way. I would have loved to compare it and the 3.Ai in detail, but didn't have more than a few minutes because I needed to catch my flight. I nearly missed a flight to Amsterdam to audition two IEMs. Thanks Head-Fi! One thing is for sure though, neither the Shure or the Westone can beat the build quality and looks of the Heir!