Hi Felix - if you're adding details in 3D Coat and you're using its voxel editing mechanism, it doesn't actually make any difference if you have all quads or all triangles - when you import your polygon model into 3D coat for editing using the voxel toolset it gets converted from polygons into a voxel structure at that time, and it does not matter if you have all quads in the original polygon structure or not.

You would only want to go to "all quads" if you were going to be using a sub-d modeling toolset to do further work on the object.

Sub-d smoothing is the thing that particularly likes quad topology - voxelization does not care about it.

- Michael