Just A little different on sound stage and bass, and all the rest are quite the same.
But if you really notice the sound quality, the differences is noticeable (based on some review i read), however, the 700x is already out of ur budget ( >$100)
The 500x has much wider and deeper sound stage, more clarity, crispy high freq to me but can be considered as harsh for others, more neutral, but as i said, it is totally lack of bass.
Even i don't like bass but i still need time to get used to with it. (you can think that those bassy part at 0:10s of Spectre (lyrics ver)- Alan Walker, or 0:23s of Despacito- Luis fonsi ft Daddy Yankee is nothing for my 700x if i don't use EQ)
In contrast, shp9500s is easier to listen: more bass (still punchy but deeper), sweeter and full-er is what i can said
You should see some more review on shp9500s, because i have just listened to it for a few times (my friend once had it) so i'm can't tell you in detail of that one.
The 500x is inferred form my 700x.
Basically, you should go for shp9500s if you still want listen to music, it is a way easier to listen to or go with 500x if you play FPS all the time.
Each one have its own advantage so i don't criticize them, just let you know that shp9500s is easier to listen to. Generally, they are still top tier of entry lv in my experience.