.You need to enable “Automatic Solo” on your MIDI track, either in the “Options” sub-menu of the track context menu, or by pressing Shift+Alt+S with the track selected. When you bounce a track, it is effectively soloed until the rendering operation finishes – this mutes your MIDI track as well, which is why Drumazon never receives any note events to play and in turn outputs silence. Automatic solo sets the track to solo mode whenever another track (such as the ones with Drumazon’s audio outputs) is soloed.
There is currently no way to select multiple tracks, and thus unfortunately no way to bounce more than one track at once. This is assuming you need each output bounced separately.
If you want to bounce the entire drums section sub-mix, you can wrap your output tracks in a group track. This way you can also apply effects and automation to the entire drum mix, should you want it.
Here’s a screenshot of my usual Drumazon setup (MIDI track, drum group track with fader/meter enabled, and individual outputs):
