This is old, (back when Audio Chord Wizard first came out), but it may help explain ..

http://www.masteringmatters.com/stuff/ACW_Tempo_Map_creation.avi

Shows how to open the ACW and use it to set Tempo/Chords.
Once you have that you can add whatever you want.

If you don't need Tempo/Chords, you can simply Import the file to RB and record more tacks in free time, which sounds like it may work just as well for you if you are going to do all the additional tracks 'live'.

However, the Bar line markers at the top won't line up, which can be handy when you get to any editing or Punch-In needs.
So I usually run it thru ACW anyway just to get everything to look right and line up while I work on the project.


Make your sound your own!
.. I do not work here, but the benefits are still awesome