I'm using 2012.5 so I don't know if the older versions differ for what you want. You can change an audio track to midi and vice versa. I recently got Garritan personal orchestra. I had a Biab song with strings in the style, but wanted to use the Garritan strings instead. So I set up a blank midi track for the Aria vst and selected the strings I wanted. Then I copied the midi strings track to the Aria track. To mix just mute the tracks you don't want. Others, who a refer to as gurus, might have a better answer.

Stan


Cornet Curmudgeon