After playing a few days with my AK120 player (firmware 1.32, bought brand new for 1000$ in Bangkok during a trip) and a few pairs of IEMs (ASG-2, SE535Ltd, EPH-100, FA Adagio3), I keep coming back to the only one pairing which sounds awesome with no EQ at all: ASG-2 + AK120.
Best soundstage ever, you can pinpoint instrument position so well, this is about the only thing that allows me to dsitinguish the AK120 from my Cowon X7 using 16/44 music (which is already a feat considering how good the X7 sounds in my opinion). I'll throw in a few FLAC file to see if that helps.
Pairing with EPH-100 was also extremely good without EQ, although the Yamahas are lacking details when opposed to ASG-2 (well, different price range).
The only thing that doesn't really work well so far with this player is gapless. For some reason, activating gapless doesn't do anything... and the blank between songs is actually worse than with the X7. A bit hard given the price, but the build quality and raw sound largely make up for this.