I move your object for see the curves geneator and kill it for no problem
(normaly obj export don't take care but ...)

So Export in Obj format Weld enable : quad + triangles

In Zbrush
Menu Tool/ import the obj file (your ring)
You are in Edit Mode If not (T)
Select all except the top face (With drag rectangle selection + ctrl)
Menu Masking Inverse selection
Menu Geometry divide (I don't make division for the top)
Menu Masking Inverse selection
Menu Geometry divide (here I had divided twice)
that all ;)
iT's THE PLANE TOP FACE WHO MAKES PROBLEM
With this trick of selection all is cool! You can divide top, and all except Top separately :)

If you want more options Makepolymesh3D

Right Click and Frame for see the divisions

You can maybe control some welding if you want with these cursors TRri2 Quad and Weld