Best RPI-DAC for Car Audio

Hi guys i’m finally making this big project that i’m dreaming of from a long time and i need your help!

Here we go:
I just want to replace my OEM car headunit with a Nexus 7 and send audio with DLNA to raspberry 3 ( no wires :wink: ) using AirPlay.

Raspberry then should just PreAmp (and maybe EQ) the sound for the amplifiers.

Now to straight to the point:
I want something that has at least the same quality of a commercial headunit ( Alpine, Pioneer, … )
I’m thinking of 2 possibilities:

HifiBerry Digi+ —> Optical/Coax —> Fiio D03K —> Amplifiers
HifiBerry Dac+ —> Amplifiers

I was just thinking that with Optical cabling i’m isolating RPI from HighPower stuff ( reducing noise, protecting devices ) but i can be wrong.
What’s the best solution in your opinion?
It’s Fiio D03K better than HifiBerry Dac+?