Hi,
How do you compose with Spark ? meaning, what notes do you use to trigger the pads?
I'm using the notes C3 to D#4. Check Spark's Prefs tab and see if the MIDI section is set to Spark Drum map model.
If you get sound out of Spark when using Cubase's Piano Roll, that might be more tricky to help you, since that should mean that Spark is receiving the right notes to play the pads, so if Cubase is doing something different between its Piano Roll and its MIDI track, then maybe someone experienced with Cubase (I'm not, sorry) may have to jump in and help.