If I were looking for a better USB motion controller, based on what I'm hearing via this forum I would seriously consider the UC300 - although personally I would prefer ethernet to USB. Better ground isolation, better noise rejection. There is now an ethernet version of the UC300. However, the UC100 comes from a good company and has been around for a fair while now. Other options might need a bit more work to integrate them, although unlikely to need any rework inside the mill itself. Good luck with findind a KX3!