Welcome, Rich.
The bounce or freeze methods work for soft synths, but not for external hardware modules.
You say you are getting sound successfully from the module. Is the sound playing through an audio track in Sonar?
If so, arm the track and hit record.
You will need to record the audio output from the module real-time to your audio track.
Once that is done, you will have something to export.
I am not directly familiar with the SD50, but your signal path should be:
MIDI track>Output to SD50...SD50 Input to Audio track.
You can build complex project songs by recording different MIDI tracks to new audio tracks.
Then export the whole project.