AK100 can work with the headphones over 170 impedance approximately. The DAP has a 22 ohm OI and if you do the 1/8 rule, apart from a few Ety iems and Tzar series (esp. 350) nothing can work with it correctly, you will see/hear the effects of OI impedance the phone does't sound like it is supposed to.
AK120 seems better with it 3/5 ohm OI but still not ideal for iem/ciem world. The best is less than 1 ohm of course like DX100.