You need to specify your needs, because there are so many possibilities by dongles:
Battery inside (Y/N), DAC (delta-sigma (which chip), 1bit, R2R), Bluetooth (Y/N), Amp (discreet, chip), Volume implementation (independent hardware volume, not independent, no volume control), Display (Y/N), form-factor (maximum portability or not), etc.. etc..
Battery (Y) but ability to bypass so that I can use it connected to USB without battery degradation\constant drain
Bluetooth not a must,
AMP preferable Ig,
Display not really important,
Would prefer optionally something smaller and portable
4.4mm balanced plug preferable
I care mostly for it to drive my MK3's properly as some mentioned the treble drivers need some juice. Although I still think Apple dongle might work fine. Given that you have the mentioned IEM's maybe you'll be able to advice me well. Also I have bit conflicting views about this DAC\Amp things, some say they do nothing to the sound and that is all snake oil, some say certain DAC's are good for "gaming" to pin-point sounds better etc.. I am unsure if that is really true, I would prefer such unit which gives some benefits also for gaming.