Per your suggestion, I went to Mongkok and demoed the best IEMs I could get my hands on.
I said before in ljokerl's IEM thread that tuning an IEM in detail with a parametric EQ is like no-holds-barred total racing spec modification for a car, even something like a Toyota Supra, in racing trim, can beat a stock supercar. That turned out to be the whole truth from what I heard today.
SHE3580 A-spec (standing for the A-shaped EQ curve, and also for full-on racing tuning) went up against
Westone UM3X
Sony XBA-3
Senn IE80
JVC FXD80
And none of them except the XBA-3 got even close without the help of the 10-band EQ on Poweramp.
I played pre-EQed tracks on the SHE3580 and the unaltered tracks I just re-loaded on my phone on the challengers.
Main tracks tested were
Hotel California (from Hell Freezes Over album)
Re-Sublimity (OP to Kannazuki No Miko)
The UM3X and IE80 sounded similar: bloated bass, muffled highs. I would even put the stock SHE3580 above them. (but below the FXD80 and XBA-3)
FXD80 sounded ok, except they had amazingly boosted high highs. Not at sibilance frequency but still, they sound good for about a minute and then it's time to either dial in EQ or take the phones off or claw your ears off.
The XBA-3 was the best of the bunch for me. It gets the balance about right, and with a boost to 1kHz and 2kHz on the equalizer the timbre is also about right. Without that boost vocals sound off. Still can't compare to the SHE3580 A-spec in smoothness in the highs.
I tried to pay attention to the imaging like you said, but couldn't find anything special in them. I demoed the IE80 because DustDevil told me those are supposed to have a reputation for great imaging, well I didn't hear anything like that. If anything thanks to the instruments sounding more realistic to me on the SHE3580 A-spec, they at least gain a more realistic presence in my headstage. None of the phones gave me convincing out-of-head imaging. The XBA-3 imaging was a bit different from the rest in that the opening guitar plucks off to one side in Hell Freezes Over sounded like they came from *right next to my ear* with the XBA-3, unlike with any of the other phones. I don't consider that a merit though, and for the rest of the piece it doesn't image particularly differently, except it images a bit better than the other challengers because it has the most realistic timbre among them.