Loquah
Headphoneus Supremus
The Thinksound on1s are very good but for some reason they sound a little grainy or harsh with the Alien. Maybe because its underpowered for them? I'll listen more to confirm its not just confirmation bias.
Concur on the Mikros. Best sound for the money I've heard but comfort isn't... comfortable.
Yeah, the On1s are just on the edge of what the Alien can drive. They sound very good still, but not quite at the peak of what the On1s can deliver.
I personally don't mind the Momentum On Ears with the Alien, but I also wouldn't say they're an end-game option. I have a set of AAW A3H universal IEMs here at the moment and they're pretty impressive - like a FIDUE A83 with a little more balance across the whole frequency range so slightly less emphasis on the treble, but similar extension and detail. They pair really well with the Alien.
Of course, Noble K10s are also a great option, but so far I haven't found a source that the K10s don't love