Personally, i love the sound nature presentation of cans than iems. I have some flagship universal iems, but still i prefer on-ear cans presentation based on my personal taste. By saying this, it does not mean my tg334 / parterre is worse than let say dt1350. Technically, i feel those iems is very good or perhaps better, it just that i more prefer on/over-ear presentation , which can satisfy me more.
ES S-EM6 is good. But imo, you need special taste and get use to it to enjoy it more. To me, the signature is too creamy for my taste. It is too smooth and thick sounding iem. Detail is good. Mids is very lush. But i feel like loosing all the excitement when using this iem. But if you were a pure vocal lover, then u might like it. Between s-em6 with tg334, i would prefer tg334 with ak120 (non amped). However thou, you might want to check a much cheaper iem like um3xrc. This iem, everytime i listen through my ak120, i feel like they have a very nice synergy together. The sound is VERY nice. I compared some other iems using ak120, but i think this um3xrc could be my fav to go direct from my ak120 (flac 24bit files). For on-ear phones, from what i have, i would suggest dt1350. And if you want a warmer sound, lusher mids, thicker sound presentation, and better fitting than dt1350, you might want to try beyer t51p , but less just a bit clarity to dt1350. Momentum also nice. But personally i love signature of dt1350, it has a sense of more analog presentation than momentum. And if sound to be the only thing i should concern, i will choose dt1350 over tg334/um3xrc, through my ak120. But maybe it just me , bcoz i prefer cans than iem.