you may want to start by explaining why you feel the soundstaging on the ad700x is not good enough. they have a nice wide soundstage equal to or better than headphones in the sub $300 range. of course what kind of soundstaging you prefer will bias your opinion but its been claimed by individuals that all of the cans ad700x, dt990, k702, q701, dt880, hd800, etc have better soundstage than the rest. i think it depends on what you consider good soundstaging (some offer better close up, some offer better far out, some sound more natural while others sound a bit unnatural).
also, you may want to note what you liked and did not like about the ad700x as well as what equipment you have to power them and what purpose you want them for.