Look at the guide, if some scores an 8 or higher, you're pretty much set. Hell, 7.5 or higher. Then it's up to you to decide what kind of sound signature you would like.
There is no end be all headphone, especially not with your budget. You get something, you lose something else. If you want to analyze footsteps, get the AD700s. They have very, very little bass, so you can focus on smaller details. However, your example is too extreme, even for the AD700.
The 990s do positional audio very well.
I'm not gonna sell people BS, and claim you can hear a fly buzzing from the other side of a map with ANY headphone.
The most important thing is to have detailed headphones with large soundstages and great positional accuracy for the closest thing to god mode in terms of game audio. AD700, Q701 come to mind. Even so, it's a few percentages better than everything else that scores an 8 or so. Not night and day or even better enough to dismiss other, well balanced headphones that are more immersive.
Hmm I see. It turns out that the DT990's + DSS are too expensive for me. So I need to save up a little more.