Cubasis and Roland Duo Capture EX

Same happened this evening with the Yamaha iMX1 cable hooked to a lightning to 30 pin adapter.
I was not able to make it working with Cubasis to record some midi tracks.
Now I succeeded hter’s another issue I need to solve: how to record a track in Cubasis that will drive only an external MIDI instrument without having a piano sound (default patch) that comes out from the iPad speakers?
Do I always need to link an intenal sound to Cubasis MIDI tracks? Can these tracks drive just external instruments as if I had a traditional MIDI sequencer?
Thanks