I use Nodi not kodi a fork of Kodi 17.1. On my Zidoo x6pro works fine much beter than Zdmc or. FTMC. SO ALSO. Ino need. To wait for zdmc or buy are new box ....
4k did work, not all files, If it is more than 8GB, it may stutter if you are streaming from PC to zidoo. You can copy to thumb drive and play directly to zidoo. But still stutter if file size is higher. Btw, did you check the display under android settings. Make sure it is set to auto or 4k. Under settings -> Display, if I remember correctly.