You might want to try Band-in-a Box. "Type in the chords to any song using standard chord symbols like C or Fm7b5; and Band-in-a-Box does the rest, automatically generating a complete professional-quality arrangement of piano, bass, drums, guitar, strings and more.  Plus, add REAL accompaniment to your song with RealTracks and RealDrums- actual recordings of professional studio musicians!"
   I've recorded quite a few demos for myself and others using BIAB for backing tracks. There are many dozens of different styles from Heavy-Metal to Jazz. It's dead simple to use and I know pro composers who use it to generate ideas for film scores. It also can generate instrumental solos.
http://www.pgmusic.com/