multiple staves in staff view

The way to do this is use 2 tracks.  One for your melody (treble)  and one for your keys (treble/bass).  You can open them both together in staff view.  I do this all the time.  I create 2 "dummy" tracks...one with melody and chord changes and one with me improvising on the keys to see rhythms and such...then orchestrate from there.
 
However, you might be disappointed with Sonar's staff view abilities as they are quite basic. And this whole audio-to-midi-to-staff thing has never been great or fun to deal with on any system.
 
Usually you are better off going strait into a notation program.
 
Try downloading the Demo before you buy anything and get frustrated.