Hey there ged wright!
My work flow is almost the same but with Max.
Base mesh in max export to Obj.
Import to ZBrush divide and sculpt.
Export to Obj. at lowest subd.
Import Obj to Max and edit(pose)
Export.
Import to Zbrush works fine, then stepping up through the levels it breaks!
I have followed all the steps that sonn wrote about which solved the import itself but not the reconstruction of the subd levels.
Still a problem but thank you for answering/ much appreciated
p