DAC chip is important. It creates the music source. After creation, there is no method to improve or enhance it. All we can do is to minimize the attenuation/deterioration.
Analog circuit is even more important. It converts music source to audio signal, supply energy and do sound tuning.
Passive device (headphones, speakers) is most important. It makes audio signal to sound wave. It governs the sound to ears.
I suggest spending of money according to this order.
It is just my personal opinion. I prefer M15 rather than old AK models. New DAC chip is ahead of old DAC chips by a lot. And Fiio circuit design is good.