X3: All Synth Audio Outputs vs simple instrument track

For a simple single instrument like bass or piano, I use a simple instrument track.
 
For drums, I use the All Output options because I want the audio for kick, snare, toms, etc, on separate tracks so I can mix them, adjust EQ, vary reverb by drum, etc.
 
When you choose All Outputs, you will get a lot of outputs.  Then you go into the Session Drummer Mixer tab and choose which drum goes to which track.  For example, if you choose 1 for kick, the kick will go to the FIRST AUDIO OUTPUT (which is not necessarily Track 1 in your project).  2 for snare will send the snare audio to the second of those tracks.  All the MIDI to control the drums will be in a MIDI track that should appear after all the audio tracks.
 
You can delete any tracks you don't need.  Personally, I keep things simple and use 1=kick, 2=snare, 3=hi-hat, 4=toms (in stereo), 5=overhead/cymbals, 6=any other percussion (in stereo).
 
Some people use a lot more tracks and put each tom on a separate track, and that's fine.  I have never felt the need for that.
 
In a simple instrument track, all the drum audio comes out on the same track.  That track will have an audio tab in Inspector and a MIDI tab.  If you open Staff or Piano Roll views, naturally you will see MIDI and not audio.
 
I use several virtual drums, including Session Drummer and EZ Drummer.  If you have any more specific questions about Session Drummer, I'll have to open a project that uses it and look.
 
Best of luck.