What graphics card you using, maja? Please keep in mind that it also may be based off the connection that you’re using as a single link DVI cable is incapable of rendering at 4k 60hz. Are you sure that you’re using either a duallink DVI, Display Port 1.2, HDMI 2.0, or higher? Unfortunately either way we don’t support the setup of plugging the monitors into separate rendering devices but I would like to try to help you as much as possible.