Taking advice from a couple of Forumites I have ditched the Casio in favour of a NP-30. It was not possible to midi the Tyros to the Casio.
Following instruction in the manual I have connected the two keyboards together using two 5 pin DIN cables, hoping this would enable the lower one to split and trigger the styles. This is not working and the sounds from the lower keyboard are still coming from it's internal speakers. Any ideas? .. Fred