There’s two different machines being discussed on this thread. So a quick recap:
Mcx8000 : doesn’t use a qwerty keyboard at all
SC5000: if you plugged in a USB keyboard, then it would duplicate the functionality of the on-screen qwerty keyboard on the SC5000 touch screen.
However, the use of such an external keyboard is not supported. Some weird and wonderful combination of qwerty and function keys, modifier key etc on the external keyboard might stop a mix unexpectedly or kick-off some other odd behaviour which has never needed to be expected programmed to react to in any particular way.