How to dynamesh without filling up holes

fa2020

Hi
I've modelled the following ring model in Rhino. I'm going to add some details using ZBrush 4R8. So I exported my nurb model as OBJ file with high amount of polygones. Then I imported it in ZBrush 4R8. Because of nature of Rhino's exported files, direct sculpting messes up the mesh so I have to dynamesh it before. But dynamesh filles up all the holes. I tried to increase the resolution but the same problem still exists. Of course it gets better a little in the terms of filling holes but other messy and sharp meshes is added to the base mesh. 
Can someone please help me out to solve this issue?

sprunghunt

You need to increase the resolution even more. Dynamesh projects a grid over your mesh. If the grid is too big for the details it will just fill in the holes.

kanga

You could try Zremeshing a copy of the imported obj. Once you have a remesh you can increase the resolution by subdivide. Judging by the mesh youy would still need a pretty dense remesh mesh.

Cheerio

onionhead_o

maybe try boolean> then zremesh?