What Matt says should be noted.
But if you already have a midi melody you want to keep, then render the Melody track to wave via the VSC synth then save the whole file. Then you can return to the song file and try out the RT sax soloist - sort of "borrow" the Melody track for the RT. Then render the RT Sax soloist (if you like it) to a wave file via the VSC. And both the Midi melody and the RT are preserved as wave files.
Do you work in a sequencer or only in BIAB? If you work in a sequencer then import both of the melody wave files with the rest of the midi data. Hope that helps.

Ian

Ian
My "Original Tunes" Site
My gene pool needs more chlorine.