The whole idea was to add you own notes to RealTracks by muting a RT section and have Sforzando play your notes using a sample set of that RealTrack.
I suggested this years ago and showed how to do it:

https://www.dropbox.com/s/6krkobu3yb65wsr/RealTrack-ShinyGuitar.mp4?dl=0

Sforzando Creating Custom Solos for RealTracks Mac/Win

Sample Sets for RealTracks & RealDrums

RealTrack Bass Samples for Sforzando

I used to use the RealChart midi of a guitar solo on a sax sample to repeat a riff the guitar played in answer to the guitar.

https://youtu.be/COPSqrezqnY?t=964