My Diokos when plugged into my phone sounds like it has half the subbass it should've had as well as not having the same sense of airyness or soundstage I get when plugged into my moondrop dawn dongle. Sure it is at an listenable volume when plugged into my phone but my Chus literally sound better than the Diokos without the DAC dongle

Granted my phone is a 2018 Xiaomi so the hardware certainly isn't the best, but I'd recommend OP to go to a local audio shop and try out how does his headphones sound like with an amp first, if it still sounds the same to him then his source is good enough