IEMs or over headphone for DAP

I have HiBy R3 pro saber and want the best headphones to work with it without AMP just headphones and DAP
my budget 300-400$
IEMs or Headphone with ability to use 2.5 balanced cable
music type classic - blue jazz
I like details in the music I want to feel all details
i was thinking of FIIO FH5s but they say IEMs not good as over headphone
IEMs will better to listen when i sleep
so plz recommend IEMs also over headphone
and i will decide