Currently I’m using Audio technical ATH M50x headphone for the last couple of years and i would like to go for an upgrade.i have Fiio A3 amplifier to boost my headphone further. my budget would be 300-350$. suggest me an ideal headphone, i mostly listen to new age, Celtic, country folk, indian classical music and i rather prefer a flat response headphone rather than bass type. the headphone can be either open or closed, only the sound quality matter and im using it indoors only. New recommendations are welcome.