I just can highly recommend Melodyne too. Its really great. All the realtracks are not really perfect. The musicians, which are playing, are doing a good job and its often musically on a top level, but that doesn't mean that you can use it right away for your own production. There is a lot stuff, which need to be adjusted.
With Melodyne you can do exactly that was is needed. You can convert audio to midi , if you want, and then use vsts to play the parts. But that often doesn't make it better, because the Live-music with real instruments and a good musician sounds much better. With midi-instruments the soul is lost, especially for solos. Here comes Melodyne into the game and you can edit with this programm audio like midi. You can change, delete and edit every note , which is played by the musician. You can make it exactly to that, what you want. Thats really awesome.