1) Xiaomi Mi A1
2) Android Oreo 8.0.0 Stock
3) Not properly understanding but I'm Submitting the features Quoted By the Company "An industry leading 10V smart power amplifier
paired with the advanced Dirac HD Sound algorithm provides powerful speaker audio output and deep lows for both music and phone calls.
The independent audio amplifier supports high-
impedance headphones of up to 600Ω. " http://www.mi.com/in/mi-a1/ all specifications are there.
Well attached audio_policy.conf BTW It's audio_effects.conf
Edit:-- Its Snapdragon 625 Series mobile and it has Qualcomm Aqstic™ Support