accurate soundstage,yes. artificial soundstage,no. lot of the headphones that give a big soundstage with everything means the soundstage is artificial. not every real recording has expansive soundstage like some headphones give. lot of headphones actually are inferior to speakers when it comes to soundstage accuracy but not all. i actually heard and own headphones very close to speaker-like soundstage which is very useful for sound cue detection without being bothered but then again my oppinion is subjective to everyone here since is just my opinion. everyone is different.
i would suggest some vintage akg's for clarity and is very capable of binaural like soundstage that ''can'' get very big and open but they require some hefty power behind them since they were designed around professional equipment and 600ohm standard then. i would suggest either pair of sextetts lp for clarity and wonderful midrange and has very open soundstage or pair of akg 240df's which i think are the king of ''clarity'' and midrange accuracy and has actually bit more openness to the soundstage compared to my sextetts lp. your fiio e9 should handle them both very well tho. if not i would look into the k400's or k500's. wonderful akg headphones as well. if you don't care for big open soundstage but still has an accurate soundstage i would look into the beyer dt48A or dt48S. they been known for the best midrange around and the first headphone made in the 1930's and still made today by beyerdynamic under special order. the tesla tech used in the T1 is actually based off the dt48 models and beyer still uses ''diffused field equalization'' on some of there models(i think the dt48s is diffused field).
if not the hd600's be a great choice while the akg 702's as well if your looking for something still in retail today at your budget. i'm not a big fan of the k7xx series from akg but they still are very good. the k271 are very good as well. i never heard any grados so i can't comment on them.