I've never used REHEARSCORE specifically, however I have used SEQUENCED backing tracks for shows before....I sequenced them from the actual scores for the show.  It's nice because you have the COMPLETE score from the start orchestrated usually with the piano dominant until the group learns the songs and then I think you can selectively remove the piano note-for-note vocal line and keep the orchestrated backgrounds.  If you plan on using it for the show that's a consideration because usually singers get used to the background tracks just like singing along KARAOKE style.  The advantage I had when I sequenced shows I did, is that I can control the NUANCES for the singers - taking the stylistic liberties they might want, including tempo, the KEY they sing it in, and timing.  The BIGGEST issue with using these tracks is when you have dialogue interspersed with the music and you're not sure how long the dialogue is going to take.  BUT even with only amateur singers - I've used these tracks and they get used to knowing how much time they have to deliver the lines which are interspersed.  Advantage of having the tracks from the outset...and the six - eight weeks rehearsal they have to work with them.

This sounds like what MartyW is looking for!