The output of any VST is an Audio track.
Most VST are just one instrument so only need one audio output. But some, like Kontakt are multi instruments. TTS-1 is also mult instrument. And Drum VST's are multi too.
When you insert a VST yu can choose a few options on how many audio channels you want to use.
Midi is used as input to trigger the samples, the samples are audio.
Because most multi instrument VST's have a built in mixer you only normally need the one stereo audio output.
You can use the GUI VST mixer to add compression, EQ and effects and balance the level.
The only reason for using multiple audio channels is so you can add better quality audio plug ins for certain instruments. Example the VST's supplied reverb or compressor is very basic so you want something more upscale.