A while ago I had an issue with importing SU files into KS. I still got that, but I did find a fix.
Layers in SU are my friend now.
After importing I get some faces with wrong material to them and they are often linked to other parts that have the same material but are correct. I can not "unlinck" so I'm kinda stuck with that.
Now I put all faces on layers by material in SU. Afterwards in KS, I get nice groups that I can aply material to and it works OK this way.