Gary,
with ather F buttons you can change phrase(thig that is right word)in diferents tracks.That mean:if you dont setisfije with Bass frase in some style you can change them.For exsample:in some Balad style you dont like haw Bass play his sequence.Press F3 button and with rotation knobe couce diferent Ballad Bass who emedetly play diferent phrase.
The same I mean with ather tracks or Fs like you call them.
Diferents between Audio or Midi drums is general:Audio drums is recordet sequence from real drumer in waw format.Midi drums are simple midi information like in ather kayboards.
Ofcourse live drum sound much betther against midi sound.
So sorry about my English,but I belive you can anderstand me.