In that case just compose your scene as you would normally do in zbrush, then grab the canvas so you get the z-depth information as an alpha, and save it externally. With any luck your other application will handle 16-bit tiffs , if not, you’ll have to convert it to 8-bit, then use it in your other application as a displacement map. Actually, depending on how close you get to the coin, you could probably just use it as a bump map, its unlikely you’ll ever get close enough to require displacement.
You’ll then be able to use your other apps bump/displacement slider to control how much relief the coin seems to have.
The main thing is getting an accurate depth pass of whatever scene you’re trying to do, and zbrush makes that process very easy. Once again: compose your scene on the canvas, mrgbz grabber to convert the depth information into a high-quality alpha, then save the alpha and use in your other app.